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I fixed a parasitic drain on my car in 408 days

466 points by dmuller 3y ago

jws 3y ago
I have failed to find the parasitic draw on an RV (slower than this one, it takes a couple weeks to kill the battery). I finally got a "Top Post Battery Master Disconnect Switch", which is a little dinglebob that goes between the battery post and cable and lets you easily break the circuit. I highly recommend the $12 solution for an intermittently used vehicle.
- bombcar 3y ago
  You can also grab a trickle-charger and use that when it's at rest, which can (on modern vehicles) prevent the computer from going nuts. If you're fancy, you can even make it a quick-disconnect setup so that if you drive away with it still on, it won't break anything (or do the poor-man's version where you have the wire connected to the wheel chocks).
- overthrow 3y ago
  I thought about this but the problem with newer cars (mine at least) is killing the power wipes the memory so it won't pass an emissions check (or something like that). After my battery died I had to find an excuse to drive an extra 100 miles so I could pass emissions. On my car the emissions laws definitely caused more emissions than they saved that day.
  - sidewndr46 3y ago
    I hear this all the time, but I have never understood it. If I clear my drive cycle monitors, they are all passing again just a few miles later. Do some vehicle manufacturers just put insane constraints on the drive cycle monitors?
    - etrautmann 3y ago
      That seems reasonable since anyone could clear and tune an engine with minimum effort to pass emissions without a history requirement.
    - londons_explore 3y ago
      > Do some vehicle manufacturers just put insane constraints on the drive cycle monitors? Yes. Combine with the fact some only pass after certain conditions (eg. over 3000 revs for 10 mins, or idle for 5 mins, or only after 3 starts, only when the outdoor temperature is within this range, etc). Sometimes those conditions aren't stated in the manuals. That makes the checks passing seem more like a random process and driving more will usually make them pass, eventually. And drivers without a code reader won't know when it has passed, so they are usually instructed by mechanics to drive a long way to be sure before taking it in for a test (don't want to have to reschedule the test just because you didn't drive it enough).
      - Scoundreller 3y ago
        And some jurisdictions will pass some “not ready” codes because a proper cycle may not happen for months. A code reader really pays off sometimes to reset everything :)
    - sokoloff 3y ago
      There is a drive cycle set of requirements and it’s usually possible to clear them in under 20 miles. Trying to figure which part of the cycle isn’t accomplished yet is the challenge. I’ve chased it down on my wife’s Honda when we were trying to get it to go “Ready” the same afternoon. Usually just not doing anything unusual for a day or so of normal use is enough, but you can often query the OBD2 system to get the portion of the cycle that’s not yet complete. Just doing a long highway drive isn’t going to do more than a moderate highway drive already did.
  - ksherlock 3y ago
    I once had a car where I had to disconnect the battery to clear the check-engine light so it would pass a state inspection.
    - stuff4ben 3y ago
      That usually doesn't work anymore as mechanics can tell that you've done that when hooking up the ODBII port.
      - jxramos 3y ago
        I recently noted in my OBD2 scanner that some vehicles support the measure of miles since check engine lights were cleared or something to that extent. It made me ponder at some point in the future there is going to be regulation mandating that to pass an emissions test you must pull up to the test station with a minimal threshold mileage on the car to vet no check engine lights have tripped in that interval.
        linuxftw 3y ago
        That's already a thing. Many sensors will be in 'learn mode' and you can't pass emissions until they are fully active.
- hirundo 3y ago
  I installed a battery disconnect switch on the dashboard of my jeep. There's a spot that seems made for it. It was a $27 solution, but I don't have to pop the hood. And it solved my charge parasite problem instantly.
- rootusrootus 3y ago
  > RV I'm reminded how often people come to the RV forum trying to figure out parasitic draw. The answer almost always ends up being the propane detector. People forget it's even there. Less of an issue on newer RVs that come with at least one basic solar panel installed from the factory.
  - moffkalast 3y ago
    That's one clean burning parasitic draw I tell ya hwat.
  - pugworthy 3y ago
    Probably not an issue with more modern systems with solar panels and the detector on the house batteries.
    - driverdan 3y ago
      Very few RVs come with solar.
      - pugworthy 3y ago
        True but it does seem to be a popular DIY upgrade.
- driverdan 3y ago
  I'm surprised it didn't already have a master shut off switch next to the battery. You should always shut off / disconnect the battery when not in use because, as someone else pointed out, the propane detector will drain it.
- dclowd9901 3y ago
  You really should have one anyway. Good for emergency shutoff.
overthrow 3y ago
Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong. Without time to dig into it myself I've just been parking it with a battery tender every time I come home.
- jonmb 3y ago
  Our 1990 Miata has a parasitic drain too. We installed a battery disconnect switch that takes about 5 seconds to connect or disconnect whenever we use the car. It's a little bit of an extra hassle, but it was an easy solution.
- sh34r 3y ago
  Let me translate the second mechanic's advice into our language: "Have you tried turning it on and off again?" How much of your clients' time (and therefore money) would you spend chasing down a bug in software with an unknown root cause, which never appears as long as operations schedules a restart every couple of days? Software engineers are all too happy to dive into those rabbit holes, but that's because we don't usually have to look working stiffs in the eye and hand them the bill for our services. That's likely not an incompetent or lazy mechanic. It's an honest one who doesn't believe they can solve your problem at a price you'd accept. The first mechanic, on the other hand, I'm a lot more suspicious of. Did they bother testing the battery before replacing it?
- darrenkopp 3y ago
  have similar issue with 2011 nissan maxima w/ key fob. guess i have a new weekend project on my hands.
- kccqzy 3y ago
  > it's normal for the battery to die if you don't drive it for 3 days I've heard this nonsense a couple times now. I was incredulous at first but everyone seems to say this. What are anyone's suggestions for a weekend-only car? (I bike to work so I don't need a car on weekdays.) Trickle charge the car battery on weekdays?
blobbers 3y ago
Is it possible the key fob just needs replacement and is causing the intermittent sleep failure?
- leviathant 3y ago
  That's probably what the author was thinking in February 2022 when they removed the batteries from their keyfob and only used the metal backup key, only to have the problem resurface less than a year later. It's probably safe to say that without batteries, the fobs were having no effect on the keyless system housed within the car.
- instaclay 3y ago
  I was also curious about this. Maybe the keyless entry computer stays awake to try to sync with a fob and then sleeps on success? If a user chooses not to use a fob at all, maybe it stays awake indefinitely trying to find a key to sync with.
  - Captaffy 3y ago
    From my own experience I believe the issue is that when these modules start to go bad they fail to turn off and stay awake indefinitely.
  - blobbers 3y ago
    Yeah sleep-wake problems often are related to things missing or broken in the (poorly constructed) system. If the software on the car was poorly written, it may not have had a good back-off on the fob check, or if the fob itself was malfunctioning it may have left the car in a weird state. While I wouldn't expect a fob to drain a car, it certainly doesn't seem implausible, especially given what the fix is.
- fullstop 3y ago
  Thinking this through a little bit further, I am wondering if subsystems can wake up if someone else uses their fob but the key signal doesn't match. Surely, at some level, something has to wake up to validate this.
Captaffy 3y ago
Had the same problem recently with a 2011 Mercedes. Didn’t figure it out until eventually the Keyless Go module (which allows push to start and automatic door unlocking) died. This fixed the parasitic drain. Apparently when these sorts of modules are dying they fail to turn off and drain the battery by constantly searching for the key fobs. Incidentally while the battery drain was going on the key fob batteries were dying extremely quickly as well, also suggesting a lot more communication than normal was occurring.
1970-01-01 3y ago
Intermittent car issues are the worst! Related is the 'My car hates vanilla ice cream' story: https://web.archive.org/web/20060213052358/http://www.campbells.org/Rant+Rave/r+r_VanillaIcecream.html https://web.archive.org/web/20060213052358/http://www.campbe...
- netsharc 3y ago
  Maybe I've read this before, but I guessed by the problem description that the answer probably had something to do with time...
- teddyh 3y ago
  That’s an old urban legend: https://www.snopes.com/fact-check/cone-of-silence/ https://www.snopes.com/fact-check/cone-of-silence/
localhost 3y ago
While not a fix for this problem, a nice form of insurance is a Lithium Ion jump start battery[1]. I'm amazed that a hand-held battery can discharge fast enough to jump start my car, but ... it works great. [1] https://www.amazon.com/dp/B0B55RFM1Z https://www.amazon.com/dp/B0B55RFM1Z
- tokamak-teapot 3y ago
  Might the battery charge a capacitor?
- tvarghese7 3y ago
  Yeah she had one of these too.
ceautery 3y ago
This is type of thing I've seen Eric O. over at South Main Auto[1] fix in dozens of videos. Mad troubleshooting skills, works hard to find root causes of things. He's pretty amazing, hidden away in some no-account town in upstate NY. 1 - https://www.youtube.com/@SouthMainAuto https://www.youtube.com/@SouthMainAuto
- gooseyard 3y ago
  I really enjoy his channel- another good one is the Pine Hollow Auto Diagnostics channel, which has dozens of really involved parasitic draw diagnoses, have learned a great deal from that one.
- bityard 3y ago
  Although I perform as much of my own auto maintenance as I can, I watch Eric O because he's entertaining, and all of the technical wisdom and advice just comes along for the ride.
- ldoughty 3y ago
  Man, I would love for him to look at my 2003 Ford Ranger. I turned on the headlights and the anti-lock breaks engaged and the gauges randomly fluctuated. That's the most recent 'fun' story I have with it... Had a parasitic drain in this thing for 5+ years, but it operates 100% fine as long as I keep the battery charged with a tickle charger and can avoid jumping it. I've mentioned this to nearly every mechanic in the last 5+ years, no one has ever found the issue. Three said replace the battery, 1 said get a new alternator. Seems like those 2 would be the go-to for mechanics these days.
  - 1970-01-01 3y ago
    Check your ground wires, especially when you flip the light, honk the horn, or anything that is relatively high current. Corrosion on a wire can be fixed with Deoxit spray.
mysql 3y ago
I used to be a computer engineer working on embedded systems for automobiles. Quiescent current is what the normal proper draw is called for these systems when the car is off. We worked very hard getting these numbers in spec but it was hard to catch everything especially in this case where the issue is probably due to software missing the sleep state for that module. This could be from bad code or your CAN/LIN bus is messed up in your car. 99% of mechanics (and engineers) have no idea where to start with debugging these issues and the answer will be "replace the module".
- xattt 3y ago
  > This could be from bad code or your CAN/LIN bus is messed up in your car. If the car had been operational for years and years, why would bad code crop its head now?
  - toast0 3y ago
    Some counter finally overflowed. And now the new value is less than the old one, which breaks something, etc, etc.
everybodyknows 3y ago
Anecdata: Some Hondas (e.g . 2010 Element) exert enough parasitic drain to put the car into a chronically undercharged state if a door is left ajar overnight. The wrong thinking turned out to be: Car is safe in garage, interior lights go off, and my hands are full now -- why bother going back to the door to shut it completely?
- porkbeer 3y ago
  Never seen this issue with any hondas, including elements, sure you got a good battery? But leaving a door ajar is user error.
discardedrefuse 3y ago
Thanks for this timely post. I'm literally in the middle of running down a parasitic drain on my Nissan Xterra. I tracked mine down using a different method which helps when your fuses don't all have test points (and no conversion table needed). - Disconnect negative battery cable - Switch your multimeter to 10A (don't forget to swap lead ports) - Connect the multimeter in-line between the negative cable and negative battery post - The readout on the multimeter should now tell you how much drain you have - Start pulling fuses one by one until you see the amps drop to normal
- Scoundreller 3y ago
  And pro-tip if you need to go down the line past the fuse box: if you have a DC clamp-on ammeter, you can do multiple windings to 2x or 3x the current readings for smaller draws that the clamp-on might not pick up on.
  - justnotworthit 3y ago
    Whoa, thank you. I was disappointed to read in my multimeter's manual (klein CL800) that the resolution for DC (up to 60A, if I'm reading "range" in the chart correctly) was only 10mA.
vivalibre 3y ago
There is a YouTube channel that has a lot of excellent content on finding and fixing parasitic electrical draws. Pine Hollow Auto Diagnostics. nb: I am not affiliated with this chan, just a fan.
benatkin 3y ago
He should move to San José.
insane_dreamer 3y ago
> Dealer: said my car was fine and returned it to me. My car died the next morning. Least surprising finding
ciscoriordan 3y ago
I had a parasitic drain on my Tacoma from my Automatic device (OBD-II reader / GPS tracker). I parked in a garage with no cell service and it drained the battery by constantly trying to connect. It was a non-issue when I commuted daily but started killing the battery when COVID happened and I switched to WFH. Hard for mechanics to diagnose because they had no idea what that device was and also one of their first steps was to unplug it, put it in a cupholder, and plug their own OBD-II reader in. Now the Tacoma is parked again most of the time because I got a Tesla and I'm noticing a voltage drop. I need to do more research, I don't know if this is normal for being parked or if there's a drain.
karolist 3y ago
My father (a professional auto mechanic) took about 6 months to find a random engine shutoff during harder cornering in his Toyota, the culprit was a damaged inner insulation layer for a few wires within the wrapped wiring harness for the ECU, engine moving on the engine mounts would sometimes cause a slight harness shift and a short would cause a hard reset of the ECU. Another story I have is my computer geek friend finding an issue with my Subaru Legacy, when no other mechanic could (I tried 3). The issue was that the car was old, first gen OBD, he downloaded some legacy asm ECU reader and made a diagnostic cable from spare parts, the issue was that the car would not start when cold, or be extremely hard to start. The culprit was damaged wire that tells the ECU that the engine is in cranking condition, therefore needs a different fuelling mode, without seeing this mode there was not enough fuel to start when cranking. Eventually this was found by hooking up an oscillograph to see the injector impulse length (duty cycle), as the old gen. diagnostic didn't show any errors, he compared a working car injectors to mine when cranking cold and found this. 10 years later I'm still amazed by his skill and dedication, I'd have scrapped the car otherwise. The car was sold eventually to another person who restored it (rust repair mostly) and his wife still drives it to this day, a 1994 Subaru Legacy.
- ryandrake 3y ago
  Your friend’s fuel issue seems a lot like the intermittent no-start, low fuel pressure issue I have been debugging (3-series) for over a year now. It has defeated three dealerships and two independent mechanics so far, so I’m taking over the diagnosis now. No clue yet but today’s cars have too damn many computers in them.
  - karolist 3y ago
    which engine is that? I had an N54 335 for 5 years too, even E36 era BMWs have vastly superior error logging compared to JDM from that vintage. I hope you find your issue, but if it defeated dealerships it sounds troublesome. Log some live data with INPA if it's an older one, I have no experience with BMWs post EXX series to drop any advice...
    - 3y ago
zwieback 3y ago
Not just for highly computerized cars, I have a 97 Ranger where literally everything is manual and I don't even have a dome light anymore. There's a parasitic drain I can't quite figure out so I just make sure to start it every once in a while. Since I'm a year round bike commuter the truck can sit around for a long time, especially in winter when there's no house and garden projects. I've considered adding a manual battery disconnect, the only thing I'd lose are the pre-programmed radio stations.
- Scoundreller 3y ago
  Solar panel? Depends how big the draw is.
  - zwieback 3y ago
    Good idea, solar panel for trickle charge. Could power a few other things like a wildlife cam and weather station.
  - rapjr9 3y ago
    After the pandemic started I was using my car about once a month or two and the battery was getting drained enough that the car would not start. This solar panel fixed that problem: https://www.amazon.com/gp/product/B07Y5TKMZ4 https://www.amazon.com/gp/product/B07Y5TKMZ4 It is powerful enough to actually charge the battery instead of just maintain it, and it has a charge controller so it won't overcharge the battery. It did fail me once when we had a couple months of rain and overcast weather, but kept the car going otherwise. Eventually replaced the battery with an AGM battery and that plus the solar charger has worked very well.
mbfg 3y ago
South Main Auto has an excellent youtube channel with various parasitic draw videos. For those struggling, it's a good watch. Here's one such: https://www.youtube.com/watch?v=qDqlG5bRq8k https://www.youtube.com/watch?v=qDqlG5bRq8k
- rrmm 3y ago
  Second this suggestion for anyone working through parasitic draw issues. He has a very solid, logical process for working through this (among other issues). I always enjoy watching the videos because it's like watching a who-dun-it where you're trying to guess the cause as he gathers evidence.
Gordonjcp 3y ago
I found that my old (1997) Range Rover would flatten its battery after being parked outside my house over a weekend. If I didn't drive it for two or three days, it would be too flat to start. It turns out that the BECM (body ECU) wakes up from sleep if it hears anything coming in from the RF keyfob receiver, on 433.92MHz, a standard ISM frequency. If it's not a valid fob code (and there is a surprisingly complex rolling code sequence) it'll go back to sleep after 20 minutes or so. The oil tank gauge for my central heating had a remote sensor that... yup. Transmitted on 433.920MHz, of course. The aerial for the keyfob is on the rear right corner of the vehicle, the oil tank for the heating was on the left-hand side of the driveway right at the back of the house, so when I backed into my driveway it was right beside the receiver. I managed to do just fine with popping the lid off the oil tank once a month and looking inside to see how much fuel was left, having taken the battery out of the tank sender.
- 83 3y ago
  Can't recall where, but I recently learned this was a common issue at airports in the early days of wireless key fobs. The radar sweep at the airport would wake up the receivers causing cars parked there for a while to have dead batteries.
nuancebydefault 3y ago
Once you find the fuse that passes the highest current, why not just place a switch button in series with it? Turn it off when exiting the car. Add an LED to show when it is on.
- falcolas 3y ago
  Personally, I'd go for a relay on a non-problematic circuit. But I also get why you might just leave it disconnected - if it's pulling a few more amps with no clear cause, what is going to go wrong with it next, and what vital system will it take with it?
  - nuancebydefault 3y ago
    Oh a relay that goes on after you turned the key would be very handy. It is rather easy to find a point where there's only a voltage present after/while starting. Of course, when the array controlled circuit would be vital for entering or starting, this would not be an option.
- Scoundreller 3y ago
  If you’re going to do all that, just rewire it so the circuit only turns on with key-on.
- tvarghese7 3y ago
  It was not all that easy to get to and not all that easy to mount a switch securely near by. May be I just lacked imagination. The real reason and the part I skipped was the leakage current was getting worse over time. By the time I replaced the MICU it was close to 2A draw. It was just a matter of time before it died.
binkHN 3y ago
Had a similar issue with a 1.5-year-old vehicle that would have the battery fully drained in a little over a week if the vehicle wasn't driven. Had the dealership "fix" the problem three times and the problem was never fixed. I used the lemon law to get a brand new vehicle. I won't name the brand, but dealing with the manufacturer for this was rather trouble free.
- sizzle 3y ago
  Name and shame, help your fellow HN readers out, no shame in getting a lemon!
arscan 3y ago
Wow, I have a 2012 Mazda3 and have the same problem, which only really surfaced during the pandemic when I stopped driving my car regularly. The dealer said it was just a normal level of drain (even though it would die in just 4 days of non-use) and I should get a trickle charger. Which I did, and is annoying, but is something that I can deal with. I’m not sure if I’m willing to disconnect my remote entry to see if this fixes it, but I’m glad others have seen similar behavior because it really bugs me that the mechanics would just shrug and not really diagnose why this was happening.
williamDafoe 3y ago
We have a similar problem with a Lexus rx300 2001. The computer never goes to sleep. I was thinking of looking for (or making) a patch-fuse with a kill switch to stop the drain. Computer sleep depends on the flakey door controller switches.
bruiseralmighty 3y ago
My current driver is a pre-2010 vehicle. I really don't want to buy any of these newer cars. Maybe I can import one from Cuba.
maherbeg 3y ago
Well this is entertaining. Our 2012 Mazda CX-7 seems to die if we don't drive it for a week. I've sort of ignored this problem but now I'm going to go check some fuses and see if this is the same problem.
KingMachiavelli 3y ago
I've never understood why cars don't just cut power before the battery is too low to start. If that's too complicated then just have an option to cut all power after X hours of non-running time. I bet the old popular theft of car radio is a root cause; cars needed to stay running to keep the alarm active and power the radio continuously so it wouldn't require the unlock code every time you start the vehicle. It's actually pretty impressive how much power even a 200mA draw at 12V is over a few days; it's about 58 Watt-hours or 3.5 iPhone batteries per day.
- topspin 3y ago
  > I've never understood why cars don't just cut power before the battery is too low to start. The design of most cars can't tolerate losing 12V DC power without problems. Clearing superfluous codes after a battery swap is SOP. Cars are build for two simultaneous customers: regulatory regimes and work-a-day 13.5K miles a year workers that start (and thus charge) their cars at least every 48-72 hours. Other use cases aren't really considered. Some are better than others though. I have a 21 year old Nissan with a factory alarm and key fobs that sits for a month or more and starts fine every time. Heating helps a lot.
  - topspin 3y ago
    Something I forgot to mention here that supports my view that designers of modern cars are not thinking about this problem at all: after battery power is lost cars lose their maps and tables for ignition timing and fuel delivery. After a usually short period of time (20 minutes is typical) that data is lost and the engine etc. has to 'relearn' when the power is restored and the vehicle is operated for a time.
- pvaldes 3y ago
  > why cars don't just cut power before the battery is too low to start. Some cars computers block the start by software if the battery is "slightly" low (even if would not be too low to start).
- bonestamp2 3y ago
  Cutting the power is easy, the hard part is for the car to know when/how to reconnect power when the driver wants to start the vehicle. I guess with a physical ignition switch, the mechanical motion of the tumbler could reconnect power. But, most cars don't have ignition tumblers anymore.
fullstop 3y ago
"Fixed" in the same way I can "fix" a stuck key on a keyboard by physically removing it. They've circumvented the problem but are left with less than what they originally had.
- d3ad1ysp0rk 3y ago
  I was hoping he'd take the module out and open it up to see what was fried/malfunctioning inside.
- Lord_Zero 3y ago
  Had to scroll down pretty far to find this. Author uses the word "fixed" everywhere but didn't actually fix anything. They just lost a feature of their car they no doubt paid quite a bit extra for on the bottom line.
- bonestamp2 3y ago
  Ya, keyless entry/start is a huge convenience. I'd be mad if I had to disable those features to use my car.
jimmytucson 3y ago
I had a similar problem with a Silverado. It is very annoying. When WFH started and I stopped driving every day, I had to jump the battery seemingly at least once a month. I had people tell me it was the battery - I knew it wasn't because I had replaced the battery a few times due to the parasitic draw emptying it over and over and wearing it out. I took it to a trusted mechanic and they told me they didn't want to fix it. I pulled all the fuses myself, one-by-one, and never figured out which one was the problem.
legitster 3y ago
I feel pretty handy with car repair stuff, but "intermittent electrical problems" are the absolute worst. In this case they were pretty lucky to trace it to a specific module. You have miles of cables in a car and and most of them are completely inaccessible. There are never any fun, happy, clever troubleshooting stories. You always feel robbed of your time. This isn't a new problem either - ask anyone who tried dealing with a British roadster. It's also why I stay far away from used cars with aftermarket accessories.
grokx 3y ago
In the 00s, my dad had an issue with the infotainment system of its Peugeot 407 that would no longer boot. An official Peugeot mechanic told him that it would cost something like 4200€ to replace the unit, so he asked me if I could have a look. After a quick search, I found an update for his system, burn it on a CD, and put the CD into its car. The system updated, and then would work normally. Problem fixed for one hour of my time and a CD.
- Scoundreller 3y ago
  A lot of dealership mechanics are mindless flowchart followers that aren’t even allowed to use their brain. Though I’m surprised “update” wasn’t a part of that official flowchart. Have had dealership mechanics ignore my notes and identify a part as being failed despite my method of 100% excluding that part as being bad.
  - porkbeer 3y ago
    Theybare because they are trained to be. You are actively dissuaded from any diag work, because it can be harder to justify your hours to the customer and dealerships are awful. For a mechanic, its a good and bad job. Nevermind ASE certification that encourages the same. Only small indie mechanics have the freedom to do good work.
sixstringtheory 3y ago
Hah. I’ve replaced the battery in our Subaru Outback on average once per year, which is way too high for this environmental minded person. I just went out last night to grab something from the car and it was making a loud electrical whirring noise. I had driven it several hours prior, no idea how long it had been going. I recorded a video and it is clearly audible. I started it and turned it off again, and the noise stopped. Friend of mine (and several other commenters here) has an old pickup with a switch on the steering column that cuts the circuit at the battery, I’m ready to install one on both my cars.
- sevenf0ur 3y ago
  I would check your owner's manual. Mine says not to be alarmed about noise coming from under the truck. In my case it's a fuel evaporation check.
- anamexis 3y ago
  Ugh, I've also got an Outback (2019) with a regularly dying battery. Let me know if you ever find any leads on the root cause.
  - sixstringtheory 3y ago
    One was a PEBCAK that I personally consider a design flaw: the rear gate light switch is on the ceiling at the opening of the gate (on our 2016), and the “on” position is activated by moving the switch outwards, ie towards the back of the vehicle. It had been inadvertently dragged into “on” position while unloading bikes, rafts and other outdoor gear, and then killed the battery while we were out for a couple days. Didn’t realize this was happening until returning to a drained battery on two occasions, and then observing the effect later while doing some garden work, when I finally connected the dots. I’ve since duct taped it into the “off” position.
  - ninjanicely 3y ago
    I have a 2019 Outback as well. I just went through some battery dying issues. Took it to the dealership, they said that the Onstar module (after 2-3 years) will start to malfunction and create a parasitic drain. The only fixes they have (as of a couple weeks ago) was to a) buy a new module (which are on back order because a number of peeps are having this problem) -- which will eventually break because they haven't reengineered it. b) disconnect the Onstar module via a circuit (my tweeters are on the same circuit, so I'd lose them) c) Open up the center console and only disconnect the Onstar module. I opted for C (which I was charged an hour of labor for). The tech there said to check back in every few months to see if Subaru puts out a new module that fixes the issue. Edit: The tech told me the Onstar module was a specific issue with 2019 Outback/Legacy, and that 2018 and back doesn't have that problem and in 2020 they redesigned the whole model, so the newer ones don't have that issue.
aftbit 3y ago
I have a parasitic draw on my 2004 Honda Civic back in college. All the mechanics I went to wanted to sell me a battery or alternator. I finally bought a meter with a 10A current limit and tested every fuse each time I parked. It turned out to be an issue with the magnetic AC clutch, so I drove it for 2 more years with the fuse for that component removed.
- bonestamp2 3y ago
  In hindsight, you could have put a relay on that circuit that was powered by some other circuit... so it only connected the AC clutch circuit when the vehicle was on.
  - aftbit 3y ago
    Yeah that would have been smart. What I did instead was just drive with the windows down. :) When it got too hot, I put the fuse back in, kept a jump pack in my trunk, and parked on a hill so I could pop the clutch to get a start.
antiquark 3y ago
I solved this problem on my Dad's car by installing a mechanical knife-switch on the battery terminal. Anytime it's going to be parked for more than a few days, I pop the hood and disconnect the battery.
civilized 3y ago
My wife and I gave our old car to her parents. In the subsequent years, its battery kept dying and we had to go over to their place and jump it. Never happened in the prior 7 years we'd owned the car. The mechanic said nothing wrong with the battery, but suggested there might be a parasitic drain somewhere. A few days later, we were visiting them. I looked at the car and saw the door closed, but not properly latched and ever-so-slightly ajar. You know, that half-closed thing car doors do when you don't close them hard enough. It turns out someone, possibly my son, had been not closing the door completely. This did not keep the lights on or cause any other visible sign, as it would in some cars. After I told them to slam the door fully shut, never a problem again for 2 years and counting.
- WirelessGigabit 3y ago
  My car beeps loudly and angrily at me if the doors are not 100% closed when I hit the close button on the fob.
  - gengkev 3y ago
    With my car, trying to lock the doors just doesn't work if one is left open — not always the most obvious failure mode, but it's been enough to get me to notice something's wrong.
    - noizejoy 3y ago
      > With my car, trying to lock the doors just doesn't work if one is left open for suburban single family residence dwellers with their own garage, they may not always (or ever) lock the doors while the car is parked in their locked garage.
      - WirelessGigabit 3y ago
        Which is one of the things one must absolutely do to ensure all modules go to sleep.
bityard 3y ago
One thing I haven't seen mentioned yet: If your battery is dying way sooner than it should be, and if you have _any_ aftermarket equipment installed (radio, backup cam, alarm, remote start, trailer light module), that should always be the VERY first thing to suspect. These things are not engineered to the same requirements as the OEM electronics, and if they are drawing 10s of milliamps while the car is off, that is certainly enough that you wouldn't notice an issue with a newer batter and a car being driven every day. But if your driving patterns change and the battery gets older, suddenly your battery is dying all the time and "nothing has changed."
- sizzle 3y ago
  Also 12v USB phone chargers that stay hot when the car is locked. This drove me crazy thinking it was a car issue draining the battery or alternator.
- ljf 3y ago
  This is exactly what happened to my car - I fitted a reversing sensor (this was some time ago). About a month later the battery was flat - but we didn't drive that often so I thought it might be that. Charged it and was fine for another month or so, but then it started to happen more and more frequently. I took to disconnecting the battery each time I parked up the car. It was only when I came to scrap the car (for unrelated issues) and went to remove the reverse sensors to use on another car that I saw a single thread of wire that was running off the reverse light, was causing a short. Ah well - lesson learnt!
frankus 3y ago
A recent HN post mentioned that a signal like radar from a nearby airport can sometimes be enough to kick the keyless sensor module out of sleep mode and drain the battery. (This was the one about CAN injection attacks).
IshKebab 3y ago
> Since I don’t have Mazda’s proprieratry M-MDS diagnostic tool, I couldn’t disable the keyless module in software myself. Ugh, imagine if normal computers were like that. "Since I don't have Intel's proprietary I-DBT diagnostic tool, I couldn't disable the wifi in software myself." I guess we're half way there with phones.
swamp40 3y ago
New Mechanic: Low battery is causing your low battery Ok, thanks.
irrational 3y ago
>Sometimes I wanted to pretend the problem didn’t exist more than I wanted to fix it. Story of my life.
anodyne33 3y ago
tl;dr my dealer had my car for a week to diagnose an intermittent electrical gremlin. My maddening intermittent electrical gremlin was with my new to me Mazda3. Occasionally and randomly after in the first few months I had it the throttle would "go to sleep" during normal driving. By that I mean in the process of normal driving I'd suddenly have no throttle response, the car would go to idle, and the only way to get it back was to completely get off the gas pedal and it would respond again as usual. I'm appreciative that worked, but I couldn't shake the idea that if that were to happen during hard acceleration bad things could happen. My first trip to the dealer yielded a recording in the event log of the throttle shutting off because it saw throttle and brake at the same time, an expected behavior I was told. I assured the mechanic and service manager that I was almost certain this wasn't the case, they had no other explanation, I continued to have the problem and made certain when it happened that I hadn't somehow been on both pedals. After an email to Mazda's support line with some technical details hoping to get my situation into the right hands, I got a call from the dealer asking to hang onto it until they could replicate the problem. The service manager or someone else in the shop drove it for the better part of a week, taking real time telemetry while they were in it while I was in a loaner. Turned out that the problem was the second brake switch hanging on. I found out that there's one switch that talks too the ECU and another that talks to the brake lights, the former being the culprit. Frustrating as could be, but like a good nerd I found the final diagnosis fascinating. I also wonder and would like to believe that my detailed and informed email to the mother ship made someone pass it up the line until it got into the right hands.
WillPostForFood 3y ago
This is a like a metaphor for modern life with technology parasitically draining time and energy from humanity with shit apps and buggy software while the "mechanics" refuse to even acknowledge there is a problem.
l00sed 3y ago
I did a write-up when my car battery died on the way to fish fry. Testing for parasitic draw is no fun. https://l-o-o-s-e-d.net/car-hacking https://l-o-o-s-e-d.net/car-hacking
matt-attack 3y ago
Couldn’t he have just measured the resistance of the fuse to determine the current flow? He knew the voltage drop.
Baeocystin 3y ago
Harbor Freight sells a $15 cheapie solar panel (with diode) that plugs straight in to a car's cigarette lighter that essentially 'solves' most parasitic drain problems, if you park outdoors, at least. https://www.harborfreight.com/15-watt-solar-battery-maintainer-64251.html https://www.harborfreight.com/15-watt-solar-battery-maintain... (Not all cars have ports that are live with the key off, but the panel has other ways to wire it)
umvi 3y ago
I have a 2013 Mazda 3 and I've had to replace the battery every year for the past 3 years. I wonder if I have this exact same problem? I don't want to disable the wireless key system though because I like being able to lock/unlock the car without pulling the keys out of my pocket. Is there an alternative to this workaround?
NotYourLawyer 3y ago
I had a car that would drain its battery if you let it go a week or two without driving it. I just got a trickle charger and left it connected, problem solved. Not really a great option to leave the hood up all the time if you park outside though.
abosley 3y ago
I sold my MazdaSpeed 3 due to a parasitic drain - it was at the dealership for 4 months at one point - with no resolution.
chemmail 3y ago
This guy should look into replacing the fuse/relay for that module. Sometimes the relays can get stuck. Thats what happened to my leaf as it would get a TCM error and drain the battery every 3-4 days. Finally figured it out after a year too lol.
- xattt 3y ago
  Yes, but then where is the story of struggle and sacrifice of having to use a metal key each time to unlock the car?
- dmuller 3y ago
  Hello, author here. I edited the article a bit for brevity. But, yes I started by checking all the fuses and relays. I didn't find any bad relays. Unplugging the ROOM fuse also fixed the problem, but at the expense of other interior features (like my stereo).
sizzle 3y ago
Why couldn’t he just pull a fuse sending power to one of these systems instead of dismantling the dash to get to the wiring harness?
- dmuller 3y ago
  Hello, author here. I did do as you described first---I pulled the ROOM fuse and the draw also went away. But, at the expense of more interior features (e.g. my stereo).
  - sizzle 3y ago
    Might have been easier to pull the head unit and tap into a different power relay with that fuse off then dismantle the dashboard, but my hat’s off to you on a job well done!
sizzle 3y ago
I had parasitic draw from a 12v phone adapter that wasn’t powering down when the car was locked, took me forever to realize that cheap Amazon gadget was causing issues!
- thehours 3y ago
  My issue is related to a 12v charger as well, except a little different. Sometimes the car won’t start (engine doesn’t even turn) _until_ I unplug the 12v charger. Then it starts right away. No idea why, but would love an explanation from someone knowledgeable!
  - sizzle 3y ago
    Glad it’s not just me!
anonymousiam 3y ago
This can be a problem with any modern car. I had a similar problem with my 2011 BMW, but I was partially responsible. I added a device to the CAN bus between the entertainment system and the rest of the vehicle so my passengers could watch DVDs while we were driving. When the vehicle was off, the ECU would stay awake trying to communicate with the entertainment system, which would fail because the device I added was powered off. The car was brand new and the battery died after a month. I removed (and redesigned) the device so it would provide CAN connectivity when off, but had my battery replaced (under warranty) before I re-installed it. It sucks that auto manufacturers don't consider the consequences of their design decisions. A malfunctioning (or missing) entertainment system should not cause the ECU to drain your battery.
tempestn 3y ago
Good troubleshooting. More of a workaround than a fix, but quite possibly good enough. I do wonder what it would need to work as designed though. Is there a dedicated ECU for the keyless system that that harness connects to?
honksillet 3y ago
I’ve been wondering if my old HOUSE has parasitic electrical currents but I’m not sure where to start.
- abbeyj 3y ago
  There are devices you can get to monitor each one of the circuits from the breaker panel like https://www.amazon.com/Emporia-Monitor-Circuit-Electricity-Metering/dp/B08CJGPHL9/ https://www.amazon.com/Emporia-Monitor-Circuit-Electricity-M... . This would let you narrow it down to a specific circuit. Figuring out what's connected to that circuit and actually taking up the power might be more difficult.
tvarghese7 3y ago
I had a 2005 Acura RL which had some pretty fancy electronics for its time. I gave it to my daughter a few years ago and she started reporting that the battery was dying. It would take several days to die, so at first she just jump start the car every couple of days. When she brought it home (she lives 5 hours away) I measured the current draw at >800mA when it should be <20mA. These cars have a Bluetooth handsfree module that goes bad and starts leaking power. The fix is to bake them in the oven at 350F for 5min to reflow the solder. Already did this twice and then decided to just get rid of it. So that was not the problem. She needed to get back so we figured out which fuse was the easiest to remove and she lived with that for a couple of months. In the mean time we figured out it was the MICU module, which is the module that controls all the electronic systems and security. Without this nothing works. I was told a new one would be north of $1200 and labor. If they could find one. The dealership said they would chase down the problem again for $165/hr just to be sure... And I would have to leave the car with them until they were ready. Possibly 3 weeks. I found a couple of the units on ebay for <$100. One was from a 2008 and another one that had some broken plastic on the case for from an early 2005 (same as my car). I tried the first one, nothing worked, all kinds of systems failed. I learned there was an EEPROM chip in the Honda/Acura MICUs that store the codes to make the systems work and are unique for each vehicle. The Dealership can program them for a fee. Having a full electronics lab, I swapped the chips in no time. It was better, but the starter would not engage. In desperation, I did it again on the 2005 MICU and... success! Mind you, it took >4 hours the first time to get the MICU out and 2 hours to put it back in. I did this at least five times. I got good enough at it that I could do the whole swap in less than an hour. Back and hands were not happy each time I did it for a day or two.
weq 3y ago
Mechanics are pretty big on youtube, i learnt this type of diagnosis from https://www.youtube.com/@JimmyMakingitwork https://www.youtube.com/@JimmyMakingitwork . He posts daily videos of life in the workshop, so the OP would of saved himself some time if he viewed! Repairing your car is just like programming, mechanics come in many varieties too.
nickpeterson 3y ago
My father in law bought a used Jetta that kept having the battery die. Kept going to mechanic and couldn’t find anything wrong, eventually they discovered a hidden gps device that an old dealer must have installed and forgot to remove.
rr808 3y ago
I bought an ODB bluetooth adapter. Left it in and kinda forgot about it, kept getting flat batteries. I never expected it to draw so much current.
1letterunixname 3y ago
My VW van has a parasitic drain because it's a VW with shitty wiring. The starter positive wire runs 4 m / 12 ft from the back to behind the passenger seat. I had to completely redo the dash wiring because the entire thing was a corroded flex "PCB" like the inside of an Apple II or an Atari 2600.
ejcx 3y ago
I'm happy you fixed it. I would have nearly lost my mind too. Hopefully figuring out the issue and fixing it is as rewarding as the problem was maddening
jakobsandberg 3y ago
You wouldn't need a car if you lived in San Diego - it's the most bike friendly city in the US!
WalterBright 3y ago
My experience with car mechanics is they are good with mechanical systems, but have little understanding of anything electrical, and even worse with electronics. P.S. If you're doing a bit of wiring on the car, don't use those crimp on wire connectors. They'll work ok for a year or so, and then start behaving erratically, slowly getting worse and worse. This is because the crimp is simply not tight enough, and the mating surfaces start to corrode. The best solution is to strip the wire ends, slip some heatshrink tubing over the wires, cut the plastic off the butt crimpon connector, crimp it on, solder the wires to it, move the shrink tube back over the joint and shrink it on. This goes for any crimpon connector. Also, don't use the auto wire you get at your local auto parts store for anything in the engine compartment. It won't last in the heat. You gotta get heat resistant wiring.
xyst 3y ago
Personal vehicles are getting way too complicated now. Too many electronic components that can be points of failure. Recently viewed a video on “steer by wire yoke” https://m.youtube.com/watch?v=agMrewRJTow https://m.youtube.com/watch?v=agMrewRJTow It’s very interesting but there are so many additional motors, sensors, and actuators to simulate the same experience as mechanical based steering. If you lose electronic assistance in traditional mechanical based steering, you have to apply more force as a driver and makes the experience difficult. What happens if I lose one or more components in this “steer by wire yoke”? Seems like as a driver you are shit out of luck. If you are a pedestrian, bye bye. All I want is a walkable city with public and alternative forms of transportation. All of these “car innovations” are mostly useless.
- dclowd9901 3y ago
  Well, they’re also incredibly noisy and unreliable. I’d be willing to bet most of the ecu code is simply Bayesian filters to deal with terrible sensor data. Cars are hard environments to get the kind of high fidelity readings you really need for the nitpicky engines they have now.
dclowd9901 3y ago
Electrical issues on cars are the absolute most maddening things to diagnose and fix. I’ve restored several cars and worked on every car I own and the one thing I loathe to do is figure out an electrical failure. Even in older cars, it’s a pain in the ass. I have an 89 e30 and one time the dash cluster started acting up. Essentially the tach and speedo weren’t responding (they’re not cable driven). Took out the cluster, checked all the connections, checked the wiring diagram to see if there were any potential grounding points I might want to consider. Nothing. Finally called a local bimmer indie shop and asked them what they thought and they directed me to the small reverse light switch wire that feeds down through the shifter hole into the transmission tunnel. Apparently it often rubs against the body and becomes shorted. I looked and sure enough it was bare. Patched it and all was well. This wire, mind you, is not at all on the dash cluster circuit. There’s no reverse indicator light on the cluster or anything like that. I would have never had any reason to suspect it was the problem. This is the nature of automobile electrical issues.
sjducb 3y ago
I would have fitted a dashboard mounted solar trickle charger and left it at that.
zh3 3y ago
A common reason for this (no idea on this specific case) is that the backup battery on the alarm (NiCd) is old/failed. The alarm system then keeps trying to charge it, hence the high (and possibly intermittent) drain.
sgt 3y ago
TIL most of HN is struggling with parasitic drains and dying batteries. It's a pandemic!
yellowapple 3y ago
Parasitic drains are fun. I usually "fix" them by simply disconnecting the negative battery terminal overnight (or just the specific fuse, if I know which one it is that's causing the drain). I had to jumpstart a friend's car the other day because she has one of those breathalyzer interlock thingamabobs on it, and between the constant power draw and (probably) a weak battery she had to start her car every day or else it'd be rather quickly bereft of life. Apparently there's a low power mode (hold the button for 5 seconds, then press it again to exit); hopefully that solves the issue.
jackmott42 3y ago
We had a Lexus 450h that was doing this, turned out to be the infotainment screen, which includes the backup camera, infotainment, air conditioning control, radio control etc. Replacement part: $24,000 car was worth about $8,000 at that point, so..gone.
aaronrobinson 3y ago
I have a drain on my VW Caddy Maxi but had it booked in already for a leisure battery and solar install. When the solar finishes charging the leisure battery the starter battery is then charged. And so hey presto I now have an anti-drain system and haven’t had a problem since. So if you have a parasitic drain and can’t find fix it convert your car into a camper :)

466 points by dmuller 3y ago

jws 3y ago

I have failed to find the parasitic draw on an RV (slower than this one, it takes a couple weeks to kill the battery). I finally got a "Top Post Battery Master Disconnect Switch", which is a little dinglebob that goes between the battery post and cable and lets you easily break the circuit. I highly recommend the $12 solution for an intermittently used vehicle.

bombcar 3y ago
You can also grab a trickle-charger and use that when it's at rest, which can (on modern vehicles) prevent the computer from going nuts. If you're fancy, you can even make it a quick-disconnect setup so that if you drive away with it still on, it won't break anything (or do the poor-man's version where you have the wire connected to the wheel chocks).
overthrow 3y ago
I thought about this but the problem with newer cars (mine at least) is killing the power wipes the memory so it won't pass an emissions check (or something like that). After my battery died I had to find an excuse to drive an extra 100 miles so I could pass emissions. On my car the emissions laws definitely caused more emissions than they saved that day.
- sidewndr46 3y ago
  I hear this all the time, but I have never understood it. If I clear my drive cycle monitors, they are all passing again just a few miles later. Do some vehicle manufacturers just put insane constraints on the drive cycle monitors?
  - etrautmann 3y ago
    That seems reasonable since anyone could clear and tune an engine with minimum effort to pass emissions without a history requirement.
  - londons_explore 3y ago
    > Do some vehicle manufacturers just put insane constraints on the drive cycle monitors? Yes. Combine with the fact some only pass after certain conditions (eg. over 3000 revs for 10 mins, or idle for 5 mins, or only after 3 starts, only when the outdoor temperature is within this range, etc). Sometimes those conditions aren't stated in the manuals. That makes the checks passing seem more like a random process and driving more will usually make them pass, eventually. And drivers without a code reader won't know when it has passed, so they are usually instructed by mechanics to drive a long way to be sure before taking it in for a test (don't want to have to reschedule the test just because you didn't drive it enough).
    - Scoundreller 3y ago
      And some jurisdictions will pass some “not ready” codes because a proper cycle may not happen for months. A code reader really pays off sometimes to reset everything :)
  - sokoloff 3y ago
    There is a drive cycle set of requirements and it’s usually possible to clear them in under 20 miles. Trying to figure which part of the cycle isn’t accomplished yet is the challenge. I’ve chased it down on my wife’s Honda when we were trying to get it to go “Ready” the same afternoon. Usually just not doing anything unusual for a day or so of normal use is enough, but you can often query the OBD2 system to get the portion of the cycle that’s not yet complete. Just doing a long highway drive isn’t going to do more than a moderate highway drive already did.
- ksherlock 3y ago
  I once had a car where I had to disconnect the battery to clear the check-engine light so it would pass a state inspection.
  - stuff4ben 3y ago
    That usually doesn't work anymore as mechanics can tell that you've done that when hooking up the ODBII port.
    - jxramos 3y ago
      I recently noted in my OBD2 scanner that some vehicles support the measure of miles since check engine lights were cleared or something to that extent. It made me ponder at some point in the future there is going to be regulation mandating that to pass an emissions test you must pull up to the test station with a minimal threshold mileage on the car to vet no check engine lights have tripped in that interval.
      - linuxftw 3y ago
        That's already a thing. Many sensors will be in 'learn mode' and you can't pass emissions until they are fully active.
hirundo 3y ago
I installed a battery disconnect switch on the dashboard of my jeep. There's a spot that seems made for it. It was a $27 solution, but I don't have to pop the hood. And it solved my charge parasite problem instantly.
rootusrootus 3y ago
> RV I'm reminded how often people come to the RV forum trying to figure out parasitic draw. The answer almost always ends up being the propane detector. People forget it's even there. Less of an issue on newer RVs that come with at least one basic solar panel installed from the factory.
- moffkalast 3y ago
  That's one clean burning parasitic draw I tell ya hwat.
- pugworthy 3y ago
  Probably not an issue with more modern systems with solar panels and the detector on the house batteries.
  - driverdan 3y ago
    Very few RVs come with solar.
    - pugworthy 3y ago
      True but it does seem to be a popular DIY upgrade.
driverdan 3y ago
I'm surprised it didn't already have a master shut off switch next to the battery. You should always shut off / disconnect the battery when not in use because, as someone else pointed out, the propane detector will drain it.
dclowd9901 3y ago
You really should have one anyway. Good for emergency shutoff.

overthrow 3y ago

Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong. Without time to dig into it myself I've just been parking it with a battery tender every time I come home.

jonmb 3y ago
Our 1990 Miata has a parasitic drain too. We installed a battery disconnect switch that takes about 5 seconds to connect or disconnect whenever we use the car. It's a little bit of an extra hassle, but it was an easy solution.
sh34r 3y ago
Let me translate the second mechanic's advice into our language: "Have you tried turning it on and off again?" How much of your clients' time (and therefore money) would you spend chasing down a bug in software with an unknown root cause, which never appears as long as operations schedules a restart every couple of days? Software engineers are all too happy to dive into those rabbit holes, but that's because we don't usually have to look working stiffs in the eye and hand them the bill for our services. That's likely not an incompetent or lazy mechanic. It's an honest one who doesn't believe they can solve your problem at a price you'd accept. The first mechanic, on the other hand, I'm a lot more suspicious of. Did they bother testing the battery before replacing it?
darrenkopp 3y ago
have similar issue with 2011 nissan maxima w/ key fob. guess i have a new weekend project on my hands.
kccqzy 3y ago
> it's normal for the battery to die if you don't drive it for 3 days I've heard this nonsense a couple times now. I was incredulous at first but everyone seems to say this. What are anyone's suggestions for a weekend-only car? (I bike to work so I don't need a car on weekdays.) Trickle charge the car battery on weekdays?

blobbers 3y ago

Is it possible the key fob just needs replacement and is causing the intermittent sleep failure?

leviathant 3y ago
That's probably what the author was thinking in February 2022 when they removed the batteries from their keyfob and only used the metal backup key, only to have the problem resurface less than a year later. It's probably safe to say that without batteries, the fobs were having no effect on the keyless system housed within the car.
instaclay 3y ago
I was also curious about this. Maybe the keyless entry computer stays awake to try to sync with a fob and then sleeps on success? If a user chooses not to use a fob at all, maybe it stays awake indefinitely trying to find a key to sync with.
- Captaffy 3y ago
  From my own experience I believe the issue is that when these modules start to go bad they fail to turn off and stay awake indefinitely.
- blobbers 3y ago
  Yeah sleep-wake problems often are related to things missing or broken in the (poorly constructed) system. If the software on the car was poorly written, it may not have had a good back-off on the fob check, or if the fob itself was malfunctioning it may have left the car in a weird state. While I wouldn't expect a fob to drain a car, it certainly doesn't seem implausible, especially given what the fix is.
fullstop 3y ago
Thinking this through a little bit further, I am wondering if subsystems can wake up if someone else uses their fob but the key signal doesn't match. Surely, at some level, something has to wake up to validate this.

Captaffy 3y ago

Had the same problem recently with a 2011 Mercedes. Didn’t figure it out until eventually the Keyless Go module (which allows push to start and automatic door unlocking) died. This fixed the parasitic drain. Apparently when these sorts of modules are dying they fail to turn off and drain the battery by constantly searching for the key fobs. Incidentally while the battery drain was going on the key fob batteries were dying extremely quickly as well, also suggesting a lot more communication than normal was occurring.

1970-01-01 3y ago

Intermittent car issues are the worst! Related is the 'My car hates vanilla ice cream' story: https://web.archive.org/web/20060213052358/http://www.campbells.org/Rant+Rave/r+r_VanillaIcecream.html https://web.archive.org/web/20060213052358/http://www.campbe...

netsharc 3y ago
Maybe I've read this before, but I guessed by the problem description that the answer probably had something to do with time...
teddyh 3y ago
That’s an old urban legend: https://www.snopes.com/fact-check/cone-of-silence/ https://www.snopes.com/fact-check/cone-of-silence/

localhost 3y ago

While not a fix for this problem, a nice form of insurance is a Lithium Ion jump start battery[1]. I'm amazed that a hand-held battery can discharge fast enough to jump start my car, but ... it works great. [1] https://www.amazon.com/dp/B0B55RFM1Z https://www.amazon.com/dp/B0B55RFM1Z

tokamak-teapot 3y ago
Might the battery charge a capacitor?
tvarghese7 3y ago
Yeah she had one of these too.

ceautery 3y ago

This is type of thing I've seen Eric O. over at South Main Auto[1] fix in dozens of videos. Mad troubleshooting skills, works hard to find root causes of things. He's pretty amazing, hidden away in some no-account town in upstate NY. 1 - https://www.youtube.com/@SouthMainAuto https://www.youtube.com/@SouthMainAuto

gooseyard 3y ago
I really enjoy his channel- another good one is the Pine Hollow Auto Diagnostics channel, which has dozens of really involved parasitic draw diagnoses, have learned a great deal from that one.
bityard 3y ago
Although I perform as much of my own auto maintenance as I can, I watch Eric O because he's entertaining, and all of the technical wisdom and advice just comes along for the ride.
ldoughty 3y ago
Man, I would love for him to look at my 2003 Ford Ranger. I turned on the headlights and the anti-lock breaks engaged and the gauges randomly fluctuated. That's the most recent 'fun' story I have with it... Had a parasitic drain in this thing for 5+ years, but it operates 100% fine as long as I keep the battery charged with a tickle charger and can avoid jumping it. I've mentioned this to nearly every mechanic in the last 5+ years, no one has ever found the issue. Three said replace the battery, 1 said get a new alternator. Seems like those 2 would be the go-to for mechanics these days.
- 1970-01-01 3y ago
  Check your ground wires, especially when you flip the light, honk the horn, or anything that is relatively high current. Corrosion on a wire can be fixed with Deoxit spray.

mysql 3y ago

I used to be a computer engineer working on embedded systems for automobiles. Quiescent current is what the normal proper draw is called for these systems when the car is off. We worked very hard getting these numbers in spec but it was hard to catch everything especially in this case where the issue is probably due to software missing the sleep state for that module. This could be from bad code or your CAN/LIN bus is messed up in your car. 99% of mechanics (and engineers) have no idea where to start with debugging these issues and the answer will be "replace the module".

xattt 3y ago
> This could be from bad code or your CAN/LIN bus is messed up in your car. If the car had been operational for years and years, why would bad code crop its head now?
- toast0 3y ago
  Some counter finally overflowed. And now the new value is less than the old one, which breaks something, etc, etc.

everybodyknows 3y ago

Anecdata: Some Hondas (e.g . 2010 Element) exert enough parasitic drain to put the car into a chronically undercharged state if a door is left ajar overnight. The wrong thinking turned out to be: Car is safe in garage, interior lights go off, and my hands are full now -- why bother going back to the door to shut it completely?

porkbeer 3y ago
Never seen this issue with any hondas, including elements, sure you got a good battery? But leaving a door ajar is user error.

discardedrefuse 3y ago

Thanks for this timely post. I'm literally in the middle of running down a parasitic drain on my Nissan Xterra. I tracked mine down using a different method which helps when your fuses don't all have test points (and no conversion table needed). - Disconnect negative battery cable - Switch your multimeter to 10A (don't forget to swap lead ports) - Connect the multimeter in-line between the negative cable and negative battery post - The readout on the multimeter should now tell you how much drain you have - Start pulling fuses one by one until you see the amps drop to normal

Scoundreller 3y ago
And pro-tip if you need to go down the line past the fuse box: if you have a DC clamp-on ammeter, you can do multiple windings to 2x or 3x the current readings for smaller draws that the clamp-on might not pick up on.
- justnotworthit 3y ago
  Whoa, thank you. I was disappointed to read in my multimeter's manual (klein CL800) that the resolution for DC (up to 60A, if I'm reading "range" in the chart correctly) was only 10mA.

vivalibre 3y ago

There is a YouTube channel that has a lot of excellent content on finding and fixing parasitic electrical draws. Pine Hollow Auto Diagnostics. nb: I am not affiliated with this chan, just a fan.

benatkin 3y ago

He should move to San José.

insane_dreamer 3y ago

> Dealer: said my car was fine and returned it to me. My car died the next morning. Least surprising finding

ciscoriordan 3y ago

I had a parasitic drain on my Tacoma from my Automatic device (OBD-II reader / GPS tracker). I parked in a garage with no cell service and it drained the battery by constantly trying to connect. It was a non-issue when I commuted daily but started killing the battery when COVID happened and I switched to WFH. Hard for mechanics to diagnose because they had no idea what that device was and also one of their first steps was to unplug it, put it in a cupholder, and plug their own OBD-II reader in. Now the Tacoma is parked again most of the time because I got a Tesla and I'm noticing a voltage drop. I need to do more research, I don't know if this is normal for being parked or if there's a drain.

karolist 3y ago

My father (a professional auto mechanic) took about 6 months to find a random engine shutoff during harder cornering in his Toyota, the culprit was a damaged inner insulation layer for a few wires within the wrapped wiring harness for the ECU, engine moving on the engine mounts would sometimes cause a slight harness shift and a short would cause a hard reset of the ECU. Another story I have is my computer geek friend finding an issue with my Subaru Legacy, when no other mechanic could (I tried 3). The issue was that the car was old, first gen OBD, he downloaded some legacy asm ECU reader and made a diagnostic cable from spare parts, the issue was that the car would not start when cold, or be extremely hard to start. The culprit was damaged wire that tells the ECU that the engine is in cranking condition, therefore needs a different fuelling mode, without seeing this mode there was not enough fuel to start when cranking. Eventually this was found by hooking up an oscillograph to see the injector impulse length (duty cycle), as the old gen. diagnostic didn't show any errors, he compared a working car injectors to mine when cranking cold and found this. 10 years later I'm still amazed by his skill and dedication, I'd have scrapped the car otherwise. The car was sold eventually to another person who restored it (rust repair mostly) and his wife still drives it to this day, a 1994 Subaru Legacy.

ryandrake 3y ago
Your friend’s fuel issue seems a lot like the intermittent no-start, low fuel pressure issue I have been debugging (3-series) for over a year now. It has defeated three dealerships and two independent mechanics so far, so I’m taking over the diagnosis now. No clue yet but today’s cars have too damn many computers in them.
- karolist 3y ago
  which engine is that? I had an N54 335 for 5 years too, even E36 era BMWs have vastly superior error logging compared to JDM from that vintage. I hope you find your issue, but if it defeated dealerships it sounds troublesome. Log some live data with INPA if it's an older one, I have no experience with BMWs post EXX series to drop any advice...
  - 3y ago

zwieback 3y ago

Not just for highly computerized cars, I have a 97 Ranger where literally everything is manual and I don't even have a dome light anymore. There's a parasitic drain I can't quite figure out so I just make sure to start it every once in a while. Since I'm a year round bike commuter the truck can sit around for a long time, especially in winter when there's no house and garden projects. I've considered adding a manual battery disconnect, the only thing I'd lose are the pre-programmed radio stations.

Scoundreller 3y ago
Solar panel? Depends how big the draw is.
- zwieback 3y ago
  Good idea, solar panel for trickle charge. Could power a few other things like a wildlife cam and weather station.
- rapjr9 3y ago
  After the pandemic started I was using my car about once a month or two and the battery was getting drained enough that the car would not start. This solar panel fixed that problem: https://www.amazon.com/gp/product/B07Y5TKMZ4 https://www.amazon.com/gp/product/B07Y5TKMZ4 It is powerful enough to actually charge the battery instead of just maintain it, and it has a charge controller so it won't overcharge the battery. It did fail me once when we had a couple months of rain and overcast weather, but kept the car going otherwise. Eventually replaced the battery with an AGM battery and that plus the solar charger has worked very well.

mbfg 3y ago

South Main Auto has an excellent youtube channel with various parasitic draw videos. For those struggling, it's a good watch. Here's one such: https://www.youtube.com/watch?v=qDqlG5bRq8k https://www.youtube.com/watch?v=qDqlG5bRq8k

rrmm 3y ago
Second this suggestion for anyone working through parasitic draw issues. He has a very solid, logical process for working through this (among other issues). I always enjoy watching the videos because it's like watching a who-dun-it where you're trying to guess the cause as he gathers evidence.

Gordonjcp 3y ago

I found that my old (1997) Range Rover would flatten its battery after being parked outside my house over a weekend. If I didn't drive it for two or three days, it would be too flat to start. It turns out that the BECM (body ECU) wakes up from sleep if it hears anything coming in from the RF keyfob receiver, on 433.92MHz, a standard ISM frequency. If it's not a valid fob code (and there is a surprisingly complex rolling code sequence) it'll go back to sleep after 20 minutes or so. The oil tank gauge for my central heating had a remote sensor that... yup. Transmitted on 433.920MHz, of course. The aerial for the keyfob is on the rear right corner of the vehicle, the oil tank for the heating was on the left-hand side of the driveway right at the back of the house, so when I backed into my driveway it was right beside the receiver. I managed to do just fine with popping the lid off the oil tank once a month and looking inside to see how much fuel was left, having taken the battery out of the tank sender.

83 3y ago
Can't recall where, but I recently learned this was a common issue at airports in the early days of wireless key fobs. The radar sweep at the airport would wake up the receivers causing cars parked there for a while to have dead batteries.

nuancebydefault 3y ago

Once you find the fuse that passes the highest current, why not just place a switch button in series with it? Turn it off when exiting the car. Add an LED to show when it is on.

falcolas 3y ago
Personally, I'd go for a relay on a non-problematic circuit. But I also get why you might just leave it disconnected - if it's pulling a few more amps with no clear cause, what is going to go wrong with it next, and what vital system will it take with it?
- nuancebydefault 3y ago
  Oh a relay that goes on after you turned the key would be very handy. It is rather easy to find a point where there's only a voltage present after/while starting. Of course, when the array controlled circuit would be vital for entering or starting, this would not be an option.
Scoundreller 3y ago
If you’re going to do all that, just rewire it so the circuit only turns on with key-on.
tvarghese7 3y ago
It was not all that easy to get to and not all that easy to mount a switch securely near by. May be I just lacked imagination. The real reason and the part I skipped was the leakage current was getting worse over time. By the time I replaced the MICU it was close to 2A draw. It was just a matter of time before it died.

binkHN 3y ago

Had a similar issue with a 1.5-year-old vehicle that would have the battery fully drained in a little over a week if the vehicle wasn't driven. Had the dealership "fix" the problem three times and the problem was never fixed. I used the lemon law to get a brand new vehicle. I won't name the brand, but dealing with the manufacturer for this was rather trouble free.

sizzle 3y ago
Name and shame, help your fellow HN readers out, no shame in getting a lemon!

arscan 3y ago

Wow, I have a 2012 Mazda3 and have the same problem, which only really surfaced during the pandemic when I stopped driving my car regularly. The dealer said it was just a normal level of drain (even though it would die in just 4 days of non-use) and I should get a trickle charger. Which I did, and is annoying, but is something that I can deal with. I’m not sure if I’m willing to disconnect my remote entry to see if this fixes it, but I’m glad others have seen similar behavior because it really bugs me that the mechanics would just shrug and not really diagnose why this was happening.

williamDafoe 3y ago

We have a similar problem with a Lexus rx300 2001. The computer never goes to sleep. I was thinking of looking for (or making) a patch-fuse with a kill switch to stop the drain. Computer sleep depends on the flakey door controller switches.

bruiseralmighty 3y ago

My current driver is a pre-2010 vehicle. I really don't want to buy any of these newer cars. Maybe I can import one from Cuba.

maherbeg 3y ago

Well this is entertaining. Our 2012 Mazda CX-7 seems to die if we don't drive it for a week. I've sort of ignored this problem but now I'm going to go check some fuses and see if this is the same problem.

KingMachiavelli 3y ago

I've never understood why cars don't just cut power before the battery is too low to start. If that's too complicated then just have an option to cut all power after X hours of non-running time. I bet the old popular theft of car radio is a root cause; cars needed to stay running to keep the alarm active and power the radio continuously so it wouldn't require the unlock code every time you start the vehicle. It's actually pretty impressive how much power even a 200mA draw at 12V is over a few days; it's about 58 Watt-hours or 3.5 iPhone batteries per day.

topspin 3y ago
> I've never understood why cars don't just cut power before the battery is too low to start. The design of most cars can't tolerate losing 12V DC power without problems. Clearing superfluous codes after a battery swap is SOP. Cars are build for two simultaneous customers: regulatory regimes and work-a-day 13.5K miles a year workers that start (and thus charge) their cars at least every 48-72 hours. Other use cases aren't really considered. Some are better than others though. I have a 21 year old Nissan with a factory alarm and key fobs that sits for a month or more and starts fine every time. Heating helps a lot.
- topspin 3y ago
  Something I forgot to mention here that supports my view that designers of modern cars are not thinking about this problem at all: after battery power is lost cars lose their maps and tables for ignition timing and fuel delivery. After a usually short period of time (20 minutes is typical) that data is lost and the engine etc. has to 'relearn' when the power is restored and the vehicle is operated for a time.
pvaldes 3y ago
> why cars don't just cut power before the battery is too low to start. Some cars computers block the start by software if the battery is "slightly" low (even if would not be too low to start).
bonestamp2 3y ago
Cutting the power is easy, the hard part is for the car to know when/how to reconnect power when the driver wants to start the vehicle. I guess with a physical ignition switch, the mechanical motion of the tumbler could reconnect power. But, most cars don't have ignition tumblers anymore.

fullstop 3y ago

"Fixed" in the same way I can "fix" a stuck key on a keyboard by physically removing it. They've circumvented the problem but are left with less than what they originally had.

d3ad1ysp0rk 3y ago
I was hoping he'd take the module out and open it up to see what was fried/malfunctioning inside.
Lord_Zero 3y ago
Had to scroll down pretty far to find this. Author uses the word "fixed" everywhere but didn't actually fix anything. They just lost a feature of their car they no doubt paid quite a bit extra for on the bottom line.
bonestamp2 3y ago
Ya, keyless entry/start is a huge convenience. I'd be mad if I had to disable those features to use my car.

jimmytucson 3y ago

I had a similar problem with a Silverado. It is very annoying. When WFH started and I stopped driving every day, I had to jump the battery seemingly at least once a month. I had people tell me it was the battery - I knew it wasn't because I had replaced the battery a few times due to the parasitic draw emptying it over and over and wearing it out. I took it to a trusted mechanic and they told me they didn't want to fix it. I pulled all the fuses myself, one-by-one, and never figured out which one was the problem.

legitster 3y ago

I feel pretty handy with car repair stuff, but "intermittent electrical problems" are the absolute worst. In this case they were pretty lucky to trace it to a specific module. You have miles of cables in a car and and most of them are completely inaccessible. There are never any fun, happy, clever troubleshooting stories. You always feel robbed of your time. This isn't a new problem either - ask anyone who tried dealing with a British roadster. It's also why I stay far away from used cars with aftermarket accessories.

grokx 3y ago

In the 00s, my dad had an issue with the infotainment system of its Peugeot 407 that would no longer boot. An official Peugeot mechanic told him that it would cost something like 4200€ to replace the unit, so he asked me if I could have a look. After a quick search, I found an update for his system, burn it on a CD, and put the CD into its car. The system updated, and then would work normally. Problem fixed for one hour of my time and a CD.

Scoundreller 3y ago
A lot of dealership mechanics are mindless flowchart followers that aren’t even allowed to use their brain. Though I’m surprised “update” wasn’t a part of that official flowchart. Have had dealership mechanics ignore my notes and identify a part as being failed despite my method of 100% excluding that part as being bad.
- porkbeer 3y ago
  Theybare because they are trained to be. You are actively dissuaded from any diag work, because it can be harder to justify your hours to the customer and dealerships are awful. For a mechanic, its a good and bad job. Nevermind ASE certification that encourages the same. Only small indie mechanics have the freedom to do good work.

sixstringtheory 3y ago

Hah. I’ve replaced the battery in our Subaru Outback on average once per year, which is way too high for this environmental minded person. I just went out last night to grab something from the car and it was making a loud electrical whirring noise. I had driven it several hours prior, no idea how long it had been going. I recorded a video and it is clearly audible. I started it and turned it off again, and the noise stopped. Friend of mine (and several other commenters here) has an old pickup with a switch on the steering column that cuts the circuit at the battery, I’m ready to install one on both my cars.

sevenf0ur 3y ago
I would check your owner's manual. Mine says not to be alarmed about noise coming from under the truck. In my case it's a fuel evaporation check.
anamexis 3y ago
Ugh, I've also got an Outback (2019) with a regularly dying battery. Let me know if you ever find any leads on the root cause.
- sixstringtheory 3y ago
  One was a PEBCAK that I personally consider a design flaw: the rear gate light switch is on the ceiling at the opening of the gate (on our 2016), and the “on” position is activated by moving the switch outwards, ie towards the back of the vehicle. It had been inadvertently dragged into “on” position while unloading bikes, rafts and other outdoor gear, and then killed the battery while we were out for a couple days. Didn’t realize this was happening until returning to a drained battery on two occasions, and then observing the effect later while doing some garden work, when I finally connected the dots. I’ve since duct taped it into the “off” position.
- ninjanicely 3y ago
  I have a 2019 Outback as well. I just went through some battery dying issues. Took it to the dealership, they said that the Onstar module (after 2-3 years) will start to malfunction and create a parasitic drain. The only fixes they have (as of a couple weeks ago) was to a) buy a new module (which are on back order because a number of peeps are having this problem) -- which will eventually break because they haven't reengineered it. b) disconnect the Onstar module via a circuit (my tweeters are on the same circuit, so I'd lose them) c) Open up the center console and only disconnect the Onstar module. I opted for C (which I was charged an hour of labor for). The tech there said to check back in every few months to see if Subaru puts out a new module that fixes the issue. Edit: The tech told me the Onstar module was a specific issue with 2019 Outback/Legacy, and that 2018 and back doesn't have that problem and in 2020 they redesigned the whole model, so the newer ones don't have that issue.

aftbit 3y ago

I have a parasitic draw on my 2004 Honda Civic back in college. All the mechanics I went to wanted to sell me a battery or alternator. I finally bought a meter with a 10A current limit and tested every fuse each time I parked. It turned out to be an issue with the magnetic AC clutch, so I drove it for 2 more years with the fuse for that component removed.

bonestamp2 3y ago
In hindsight, you could have put a relay on that circuit that was powered by some other circuit... so it only connected the AC clutch circuit when the vehicle was on.
- aftbit 3y ago
  Yeah that would have been smart. What I did instead was just drive with the windows down. :) When it got too hot, I put the fuse back in, kept a jump pack in my trunk, and parked on a hill so I could pop the clutch to get a start.

antiquark 3y ago

I solved this problem on my Dad's car by installing a mechanical knife-switch on the battery terminal. Anytime it's going to be parked for more than a few days, I pop the hood and disconnect the battery.

civilized 3y ago

My wife and I gave our old car to her parents. In the subsequent years, its battery kept dying and we had to go over to their place and jump it. Never happened in the prior 7 years we'd owned the car. The mechanic said nothing wrong with the battery, but suggested there might be a parasitic drain somewhere. A few days later, we were visiting them. I looked at the car and saw the door closed, but not properly latched and ever-so-slightly ajar. You know, that half-closed thing car doors do when you don't close them hard enough. It turns out someone, possibly my son, had been not closing the door completely. This did not keep the lights on or cause any other visible sign, as it would in some cars. After I told them to slam the door fully shut, never a problem again for 2 years and counting.

WirelessGigabit 3y ago
My car beeps loudly and angrily at me if the doors are not 100% closed when I hit the close button on the fob.
- gengkev 3y ago
  With my car, trying to lock the doors just doesn't work if one is left open — not always the most obvious failure mode, but it's been enough to get me to notice something's wrong.
  - noizejoy 3y ago
    > With my car, trying to lock the doors just doesn't work if one is left open for suburban single family residence dwellers with their own garage, they may not always (or ever) lock the doors while the car is parked in their locked garage.
    - WirelessGigabit 3y ago
      Which is one of the things one must absolutely do to ensure all modules go to sleep.

bityard 3y ago

One thing I haven't seen mentioned yet: If your battery is dying way sooner than it should be, and if you have _any_ aftermarket equipment installed (radio, backup cam, alarm, remote start, trailer light module), that should always be the VERY first thing to suspect. These things are not engineered to the same requirements as the OEM electronics, and if they are drawing 10s of milliamps while the car is off, that is certainly enough that you wouldn't notice an issue with a newer batter and a car being driven every day. But if your driving patterns change and the battery gets older, suddenly your battery is dying all the time and "nothing has changed."

sizzle 3y ago
Also 12v USB phone chargers that stay hot when the car is locked. This drove me crazy thinking it was a car issue draining the battery or alternator.
ljf 3y ago
This is exactly what happened to my car - I fitted a reversing sensor (this was some time ago). About a month later the battery was flat - but we didn't drive that often so I thought it might be that. Charged it and was fine for another month or so, but then it started to happen more and more frequently. I took to disconnecting the battery each time I parked up the car. It was only when I came to scrap the car (for unrelated issues) and went to remove the reverse sensors to use on another car that I saw a single thread of wire that was running off the reverse light, was causing a short. Ah well - lesson learnt!

frankus 3y ago

A recent HN post mentioned that a signal like radar from a nearby airport can sometimes be enough to kick the keyless sensor module out of sleep mode and drain the battery. (This was the one about CAN injection attacks).

IshKebab 3y ago

> Since I don’t have Mazda’s proprieratry M-MDS diagnostic tool, I couldn’t disable the keyless module in software myself. Ugh, imagine if normal computers were like that. "Since I don't have Intel's proprietary I-DBT diagnostic tool, I couldn't disable the wifi in software myself." I guess we're half way there with phones.

swamp40 3y ago

New Mechanic: Low battery is causing your low battery Ok, thanks.

irrational 3y ago

>Sometimes I wanted to pretend the problem didn’t exist more than I wanted to fix it. Story of my life.

anodyne33 3y ago

tl;dr my dealer had my car for a week to diagnose an intermittent electrical gremlin. My maddening intermittent electrical gremlin was with my new to me Mazda3. Occasionally and randomly after in the first few months I had it the throttle would "go to sleep" during normal driving. By that I mean in the process of normal driving I'd suddenly have no throttle response, the car would go to idle, and the only way to get it back was to completely get off the gas pedal and it would respond again as usual. I'm appreciative that worked, but I couldn't shake the idea that if that were to happen during hard acceleration bad things could happen. My first trip to the dealer yielded a recording in the event log of the throttle shutting off because it saw throttle and brake at the same time, an expected behavior I was told. I assured the mechanic and service manager that I was almost certain this wasn't the case, they had no other explanation, I continued to have the problem and made certain when it happened that I hadn't somehow been on both pedals. After an email to Mazda's support line with some technical details hoping to get my situation into the right hands, I got a call from the dealer asking to hang onto it until they could replicate the problem. The service manager or someone else in the shop drove it for the better part of a week, taking real time telemetry while they were in it while I was in a loaner. Turned out that the problem was the second brake switch hanging on. I found out that there's one switch that talks too the ECU and another that talks to the brake lights, the former being the culprit. Frustrating as could be, but like a good nerd I found the final diagnosis fascinating. I also wonder and would like to believe that my detailed and informed email to the mother ship made someone pass it up the line until it got into the right hands.

WillPostForFood 3y ago

This is a like a metaphor for modern life with technology parasitically draining time and energy from humanity with shit apps and buggy software while the "mechanics" refuse to even acknowledge there is a problem.

l00sed 3y ago

I did a write-up when my car battery died on the way to fish fry. Testing for parasitic draw is no fun. https://l-o-o-s-e-d.net/car-hacking https://l-o-o-s-e-d.net/car-hacking

matt-attack 3y ago

Couldn’t he have just measured the resistance of the fuse to determine the current flow? He knew the voltage drop.

Baeocystin 3y ago

Harbor Freight sells a $15 cheapie solar panel (with diode) that plugs straight in to a car's cigarette lighter that essentially 'solves' most parasitic drain problems, if you park outdoors, at least. https://www.harborfreight.com/15-watt-solar-battery-maintainer-64251.html https://www.harborfreight.com/15-watt-solar-battery-maintain... (Not all cars have ports that are live with the key off, but the panel has other ways to wire it)

umvi 3y ago

I have a 2013 Mazda 3 and I've had to replace the battery every year for the past 3 years. I wonder if I have this exact same problem? I don't want to disable the wireless key system though because I like being able to lock/unlock the car without pulling the keys out of my pocket. Is there an alternative to this workaround?

NotYourLawyer 3y ago

I had a car that would drain its battery if you let it go a week or two without driving it. I just got a trickle charger and left it connected, problem solved. Not really a great option to leave the hood up all the time if you park outside though.

abosley 3y ago

I sold my MazdaSpeed 3 due to a parasitic drain - it was at the dealership for 4 months at one point - with no resolution.

chemmail 3y ago

This guy should look into replacing the fuse/relay for that module. Sometimes the relays can get stuck. Thats what happened to my leaf as it would get a TCM error and drain the battery every 3-4 days. Finally figured it out after a year too lol.

xattt 3y ago
Yes, but then where is the story of struggle and sacrifice of having to use a metal key each time to unlock the car?
dmuller 3y ago
Hello, author here. I edited the article a bit for brevity. But, yes I started by checking all the fuses and relays. I didn't find any bad relays. Unplugging the ROOM fuse also fixed the problem, but at the expense of other interior features (like my stereo).

sizzle 3y ago

Why couldn’t he just pull a fuse sending power to one of these systems instead of dismantling the dash to get to the wiring harness?

dmuller 3y ago
Hello, author here. I did do as you described first---I pulled the ROOM fuse and the draw also went away. But, at the expense of more interior features (e.g. my stereo).
- sizzle 3y ago
  Might have been easier to pull the head unit and tap into a different power relay with that fuse off then dismantle the dashboard, but my hat’s off to you on a job well done!

sizzle 3y ago

I had parasitic draw from a 12v phone adapter that wasn’t powering down when the car was locked, took me forever to realize that cheap Amazon gadget was causing issues!

thehours 3y ago
My issue is related to a 12v charger as well, except a little different. Sometimes the car won’t start (engine doesn’t even turn) _until_ I unplug the 12v charger. Then it starts right away. No idea why, but would love an explanation from someone knowledgeable!
- sizzle 3y ago
  Glad it’s not just me!

anonymousiam 3y ago

This can be a problem with any modern car. I had a similar problem with my 2011 BMW, but I was partially responsible. I added a device to the CAN bus between the entertainment system and the rest of the vehicle so my passengers could watch DVDs while we were driving. When the vehicle was off, the ECU would stay awake trying to communicate with the entertainment system, which would fail because the device I added was powered off. The car was brand new and the battery died after a month. I removed (and redesigned) the device so it would provide CAN connectivity when off, but had my battery replaced (under warranty) before I re-installed it. It sucks that auto manufacturers don't consider the consequences of their design decisions. A malfunctioning (or missing) entertainment system should not cause the ECU to drain your battery.

tempestn 3y ago

Good troubleshooting. More of a workaround than a fix, but quite possibly good enough. I do wonder what it would need to work as designed though. Is there a dedicated ECU for the keyless system that that harness connects to?

honksillet 3y ago

I’ve been wondering if my old HOUSE has parasitic electrical currents but I’m not sure where to start.

abbeyj 3y ago
There are devices you can get to monitor each one of the circuits from the breaker panel like https://www.amazon.com/Emporia-Monitor-Circuit-Electricity-Metering/dp/B08CJGPHL9/ https://www.amazon.com/Emporia-Monitor-Circuit-Electricity-M... . This would let you narrow it down to a specific circuit. Figuring out what's connected to that circuit and actually taking up the power might be more difficult.

tvarghese7 3y ago

I had a 2005 Acura RL which had some pretty fancy electronics for its time. I gave it to my daughter a few years ago and she started reporting that the battery was dying. It would take several days to die, so at first she just jump start the car every couple of days. When she brought it home (she lives 5 hours away) I measured the current draw at >800mA when it should be <20mA. These cars have a Bluetooth handsfree module that goes bad and starts leaking power. The fix is to bake them in the oven at 350F for 5min to reflow the solder. Already did this twice and then decided to just get rid of it. So that was not the problem. She needed to get back so we figured out which fuse was the easiest to remove and she lived with that for a couple of months. In the mean time we figured out it was the MICU module, which is the module that controls all the electronic systems and security. Without this nothing works. I was told a new one would be north of $1200 and labor. If they could find one. The dealership said they would chase down the problem again for $165/hr just to be sure... And I would have to leave the car with them until they were ready. Possibly 3 weeks. I found a couple of the units on ebay for <$100. One was from a 2008 and another one that had some broken plastic on the case for from an early 2005 (same as my car). I tried the first one, nothing worked, all kinds of systems failed. I learned there was an EEPROM chip in the Honda/Acura MICUs that store the codes to make the systems work and are unique for each vehicle. The Dealership can program them for a fee. Having a full electronics lab, I swapped the chips in no time. It was better, but the starter would not engage. In desperation, I did it again on the 2005 MICU and... success! Mind you, it took >4 hours the first time to get the MICU out and 2 hours to put it back in. I did this at least five times. I got good enough at it that I could do the whole swap in less than an hour. Back and hands were not happy each time I did it for a day or two.

weq 3y ago

Mechanics are pretty big on youtube, i learnt this type of diagnosis from https://www.youtube.com/@JimmyMakingitwork https://www.youtube.com/@JimmyMakingitwork . He posts daily videos of life in the workshop, so the OP would of saved himself some time if he viewed! Repairing your car is just like programming, mechanics come in many varieties too.

nickpeterson 3y ago

My father in law bought a used Jetta that kept having the battery die. Kept going to mechanic and couldn’t find anything wrong, eventually they discovered a hidden gps device that an old dealer must have installed and forgot to remove.

rr808 3y ago

I bought an ODB bluetooth adapter. Left it in and kinda forgot about it, kept getting flat batteries. I never expected it to draw so much current.

1letterunixname 3y ago

My VW van has a parasitic drain because it's a VW with shitty wiring. The starter positive wire runs 4 m / 12 ft from the back to behind the passenger seat. I had to completely redo the dash wiring because the entire thing was a corroded flex "PCB" like the inside of an Apple II or an Atari 2600.

ejcx 3y ago

I'm happy you fixed it. I would have nearly lost my mind too. Hopefully figuring out the issue and fixing it is as rewarding as the problem was maddening

jakobsandberg 3y ago

You wouldn't need a car if you lived in San Diego - it's the most bike friendly city in the US!

WalterBright 3y ago

My experience with car mechanics is they are good with mechanical systems, but have little understanding of anything electrical, and even worse with electronics. P.S. If you're doing a bit of wiring on the car, don't use those crimp on wire connectors. They'll work ok for a year or so, and then start behaving erratically, slowly getting worse and worse. This is because the crimp is simply not tight enough, and the mating surfaces start to corrode. The best solution is to strip the wire ends, slip some heatshrink tubing over the wires, cut the plastic off the butt crimpon connector, crimp it on, solder the wires to it, move the shrink tube back over the joint and shrink it on. This goes for any crimpon connector. Also, don't use the auto wire you get at your local auto parts store for anything in the engine compartment. It won't last in the heat. You gotta get heat resistant wiring.

xyst 3y ago

Personal vehicles are getting way too complicated now. Too many electronic components that can be points of failure. Recently viewed a video on “steer by wire yoke” https://m.youtube.com/watch?v=agMrewRJTow https://m.youtube.com/watch?v=agMrewRJTow It’s very interesting but there are so many additional motors, sensors, and actuators to simulate the same experience as mechanical based steering. If you lose electronic assistance in traditional mechanical based steering, you have to apply more force as a driver and makes the experience difficult. What happens if I lose one or more components in this “steer by wire yoke”? Seems like as a driver you are shit out of luck. If you are a pedestrian, bye bye. All I want is a walkable city with public and alternative forms of transportation. All of these “car innovations” are mostly useless.

dclowd9901 3y ago
Well, they’re also incredibly noisy and unreliable. I’d be willing to bet most of the ecu code is simply Bayesian filters to deal with terrible sensor data. Cars are hard environments to get the kind of high fidelity readings you really need for the nitpicky engines they have now.

dclowd9901 3y ago

Electrical issues on cars are the absolute most maddening things to diagnose and fix. I’ve restored several cars and worked on every car I own and the one thing I loathe to do is figure out an electrical failure. Even in older cars, it’s a pain in the ass. I have an 89 e30 and one time the dash cluster started acting up. Essentially the tach and speedo weren’t responding (they’re not cable driven). Took out the cluster, checked all the connections, checked the wiring diagram to see if there were any potential grounding points I might want to consider. Nothing. Finally called a local bimmer indie shop and asked them what they thought and they directed me to the small reverse light switch wire that feeds down through the shifter hole into the transmission tunnel. Apparently it often rubs against the body and becomes shorted. I looked and sure enough it was bare. Patched it and all was well. This wire, mind you, is not at all on the dash cluster circuit. There’s no reverse indicator light on the cluster or anything like that. I would have never had any reason to suspect it was the problem. This is the nature of automobile electrical issues.

sjducb 3y ago

I would have fitted a dashboard mounted solar trickle charger and left it at that.

zh3 3y ago

A common reason for this (no idea on this specific case) is that the backup battery on the alarm (NiCd) is old/failed. The alarm system then keeps trying to charge it, hence the high (and possibly intermittent) drain.

sgt 3y ago

TIL most of HN is struggling with parasitic drains and dying batteries. It's a pandemic!

yellowapple 3y ago

Parasitic drains are fun. I usually "fix" them by simply disconnecting the negative battery terminal overnight (or just the specific fuse, if I know which one it is that's causing the drain). I had to jumpstart a friend's car the other day because she has one of those breathalyzer interlock thingamabobs on it, and between the constant power draw and (probably) a weak battery she had to start her car every day or else it'd be rather quickly bereft of life. Apparently there's a low power mode (hold the button for 5 seconds, then press it again to exit); hopefully that solves the issue.

jackmott42 3y ago

We had a Lexus 450h that was doing this, turned out to be the infotainment screen, which includes the backup camera, infotainment, air conditioning control, radio control etc. Replacement part: $24,000 car was worth about $8,000 at that point, so..gone.

aaronrobinson 3y ago

I have a drain on my VW Caddy Maxi but had it booked in already for a leisure battery and solar install. When the solar finishes charging the leisure battery the starter battery is then charged. And so hey presto I now have an anti-drain system and haven’t had a problem since. So if you have a parasitic drain and can’t find fix it convert your car into a camper :)