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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

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?
- stocknoob 3y ago
  Or disconnect the battery (you’ll have to reset the clock, etc., which is annoying).
  - ChuckNorris89 3y ago
    Not great advice. Most new-ish cars also store the dinamic engine calibration data in ECU RAM so if you disconnect the battery you can find your engine running harsher next time. So are the values of the headlights auto leveling system and other stuff. You're also risking to reset the radio/media unit security code (on cars that aren't too new but also not super old), which if you got the car second hand and the former owner didn't save the piece of paper it came with and give it to you, tough luck unlocking it.
    - stocknoob 3y ago
      Not ideal to cut power to the entire car, but that happens anyway on every battery swap, no? If you want to get fancy you can isolate the exact fuse and switch just that: https://www.ebay.com/itm/175668177479 https://www.ebay.com/itm/175668177479 Thinking more, given how common parasitic drains are, carmakers should have all non-essential fuses in a separate subpanel section that can be easily switched off/diagnosed.
      - BenjiWiebe 3y ago
        No. Good automotive mechanics plug a little 12v power supply into the OBD port before replacing the battery, to keep the ECU/radio RAM powered.
    - pvaldes 3y ago
      There are systems that can be attached to save the parameters from the car before you disconnect the battery or even to provide electricity to the car while the battery is being checked in another room. Not common to find and most people don't need them, but they exist.
- 3y ago
peteradio 3y ago
Mechanics are like doctors: find a good one and be grateful.
rozap 3y ago
It's fairly straightforward if the car is unmodified, as everything should be fused. Multi-meter between positive terminal and positive lead and pulling each fuse to see when the drop goes away will isolate the circuit. Then you've narrowed it down pretty far and can go from there. The horrible thing is if the car is modified, and you discover an un-fused circuit.
- sokoloff 3y ago
  I’ve had unknown draws before and many times they’re not constant draws. A constant draw is easy and quick to find. A draw that only happens when some module or other wakes up is a lot harder to find.
  - flibbityflob 3y ago
    As an example, my 2017 Corolla runs the fuel pump for a while 5 hours after shutdown to test fuel system pressurization. I didn’t even know until I recently started parking it inside and I finally heard it running.
    - Arrath 3y ago
      I had to sleep in a work truck once and every hour or so it would modulate the shutters in the air vents to refresh the air in the cab or something. The click and buzz whir kept waking me up, it was quite annoying.
    - rootusrootus 3y ago
      Yeah that's pretty normal across different manufacturers, and you only hear it if you park in a quiet garage and happen to be in the garage at the moment it turns on to do it's thing. It's testing the seal of the fuel cap to make sure you aren't just venting gasoline fumes.
      - Scoundreller 3y ago
        And usually it only runs in a certain temperature range. Winter climate cars may get several months between a test.
fxtentacle 3y ago
Wow. My German car handles being parked for 3 months just fine.
- rootusrootus 3y ago
  So does my American car.
  - EricE 3y ago
    And all three of my Japanese cars too. Definitely not normal behavior.
kybernetyk 3y ago
>It seems like mechanics really don't like digging into the electrical part of the car. If you've ever seen a car's complete wiring harness you'll know why. It's not only because there's three gazillions of wires - they're also heavily insulated with tape that makes it a nightmare to access those wires in the first place.
- dylan604 3y ago
  >there's three gazillions of wires My old math teacher would deduct points for not listing the units.
  - airstrike 3y ago
    Numbers of wires
  - rzzzt 3y ago
    "Number of wires" is a unitless quantity.
  - cloudripper 3y ago
    My former English teacher would question why the age of your math teacher is relevant in this post.
    - toast0 3y ago
      Who said anything about the age of their old math teacher? You've got to learn old math and new math, presumably with different teachers.
    - dylan604 3y ago
      why are you being ageist? I have a new math teacher, therefore my previous teacher is my old math teacher.
      - vxNsr 3y ago
        Because you were being pedantic about using fake words they corrected your grammar. Former is more correct than old in this context.
lylejantzi3rd 3y ago
> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit. I can't replace it myself because it's a coded part. My mechanic won't do it because he won't confirm that's the cause. None of the other mechanics in my area have the equipment. Even the Audi dealership won't touch it because they're backed up too. So, I keep a battery jumper in the glove box and hook the battery up to a tender when I can (outdoor parking). I don't know what I'm going to do for my next car. Pretty much every car made after 2010 has coded parts and are more computer than mechanical. It does make me tempted to learn the electronics part and open a garage that focuses specifically on fixing electronic issues in modern cars.
- cwillu 3y ago
  If you can identify the fuse for the unit, it might be less annoying to pull it when parking rather than hooking up a charger.
  - lylejantzi3rd 3y ago
    That's a great idea. I can't believe I didn't think of that. Thanks!
    - jessaustin 3y ago
      Pulling fuses is a pretty reliable way to find the relevant fuse in the first place. If the battery doesn't run down while a particular group of fuses is pulled, the one you want to pull is in that group. Start with half the fuses, then narrow down. You might have to reprogram your radio channels...
      - bityard 3y ago
        I can recommend searching for "South Main Auto parasitic draw" on YouTube. The guy is a genius at electrical troubleshooting. His strategy isn't to pull fuses, it's to set the car sit for at least 30 minutes or so (with key off) and then check each fuse with a multimeter to see which has current on it, and then check everything on that circuit. Arm yourself with schematics and wiring diagrams, otherwise it'll end up being something of a wild goose chase. (The idea being if you start pulling fuses, you can "reset" various computers in the car, which may show up as a false positive. It can take up to 30 minutes or so for all the various computers in a car to all go to sleep, although it's usually only a few minutes for most cars.)
markdoubleyou 3y ago
My last car, a 2007 Acura TSX, had the same problem--it wouldn't start after 4 or 5 days (maybe 2 or 3 during the winter). This model was from the first wave of touchscreens and bluetooth. Mechanics shrugged, pointed to the tiny, underpowered battery, and told me to drive it more. Thankfully there are a lot of car enthusiast forums out there that have been plugging away on vBulletin for years. Someone on an Acura forum had figured out that the bluetooth module was always on and looking for a connection. I tried disconnecting it, and the problem was fixed.
- timlin 3y ago
  Same problem and same fix for my 2009 Acura MDX.
- bhauer 3y ago
  Same problem with our 2007 Acura TL. And we fixed it the same way.
- aksss 3y ago
  God bless online car forums. Usually just awesome, well-intentioned, and helpful people that participate, with decades of knowledge indexed. There was a year way back there when the usefulness of the forums surpassed the Chilton's manual for me entirely - probably something to do with the addition of YouTube.
brewdad 3y ago
Don't ever go back to that second mechanic.
scrlk 3y ago
> It seems like mechanics really don't like digging into the electrical part of the car Probably worth taking it to an auto electrician, rather than a mechanic.
alexchantavy 3y ago
I saw this on the Gears and Gasoline Youtube channel: https://youtu.be/XgOowUWbCdk?t=628 https://youtu.be/XgOowUWbCdk?t=628 -- looks like a lot of work to trace a parasitic drain.
- jeron 3y ago
  If you like watching amateur YouTubers rip out their hair chasing electrical problems, I recommend checking out Tavarish and Samcrac. It turns out cheap flooded auction cars have tons of those
  - toxik 3y ago
    Pine Hollow Auto Diagnostics South Main Auto Watch Wes Work musty1
    - LoganDark 3y ago
      Do you mean mustie1? I used to watch that channel all the time, super entertaining. Shows you all the cool technical bits of engine repair and maintenance without boring you to death.
      - toxik 3y ago
        I don't often have to write the channel name out, I think you may be right. I enjoy his genuine and unstressed demeanor towards the camera. Just a guy wrenching on some hardware and talking about it.
    - millzlane 3y ago
      +1 for SMA. The man clearly takes you through the troubleshooting process and his train of though.
    - weq 3y ago
      Jimmy making it work! https://www.youtube.com/@JimmyMakingitwork https://www.youtube.com/@JimmyMakingitwork lol @ Tavarish and Samcrac mentioned here, they are TV entertainers who are more concerned about drama. If you want to learn how to repair stuff, these guys are where its at ^
ilyt 3y ago
At the very least you know to which 2 mechanics you should never give your car to
bityard 3y ago
> It seems like mechanics really don't like digging into the electrical part of the car. That is certainly correct. Troubleshooting electrical issues takes a different set of skills than most mechanics are trained to deal with. Most mechanics are so busy that throwing parts at a problem is the best way to deal with issues where the cause isn't readily apparent. It's not worth their time to really dig into a difficult issue because if they spend 8 hours of shop time and try to bill that to a customer, the customer is going to just balk anyway. Better to throw a part at it, bill 1.5 hrs, send it out the door, and let the next guy deal with it. And then move on to some more profitable muffler and brake repair jobs. This is thankfully not ALL mechanics, but it certainly is a large percentage of them, IMO. (Yep, even dealerships.)
- amtamt 3y ago
  This sounds like a majority of software engineers (and their direct managers) asking to add more CPU and RAM, when software is slow, instead of analysing a problem. I guess mechanic's time is more valuable than parts.
  - c4mpute 3y ago
    I'd phrase it like: parts have a higher profit margin...
explaininjs 3y ago
In the military, the folks tasked with Mechanical maintenance of vehicles are an entirely different branch with different training, infra, etc than those tasked with Electrical maintenance of vehicles. Perhaps we need a similar dichotomy on the civilian side.
legitimayzer 3y ago
> It seems like mechanics really don't like digging into the electrical part of the car. this is like saying that computer programmers don't like digging into the proprietary and binary blobs from other vendors. I am trying to say it's not fair to blame mechanics because even if they want to dig into the electronics, the car manufacturers take active measures to prevent 'random mechanics' from digging around. I suppose there are many rational and reasonable way to justify why this is so; probably all having some form of "because safety" and "because IP of vendors".
jerrysievert 3y ago
3 days is definitely not good for an NC. That said, mine is usually around 2 months before the battery is drained. That should give you some better expectations.
- sterwill 3y ago
  2006 NC owner here with a reasonably new battery. I keep it parked in an attached garage, so no extreme cold or heat. Mine will always start after leaving it for 1 month. I probably left it for 2 months at some point in the last two years, and it started, but that feels like pushing it. The next time a mechanic tells you cars can't sit for a few days without a battery drain problem, ask how people who park at the airport get home after a two-week trip.
  - jerrysievert 3y ago
    my battery is in fairly good shape. when my nc was sitting for long periods (months), the old battery eventually gave out. I had to have it jumped once, then bought a li-on battery to jump it with just in case. the real key to long storage (beyond a trickle charger) is clean gas. right now, though, it only has to handle 2 weeks of sitting at most (in an attached garage).
micromacrofoot 3y ago
I've been to multiple mechanics, talked to roadside assistance people, posted in multiple forums, and talked to family about this problem with an old car of mine... and they all swore up and down that you should start a car if it sits longer than a weekend, maybe a week tops. They made me feel insane about it, it's one of those widely accepted things that's just not true most of the time.
- jollyllama 3y ago
  There are other reasons to do that unrelated to the electrical system of the car. You're keeping the engine and any other moving parts lubricated. You're burning fuel, so that you don't wind up with as much degraded oil.
  - micromacrofoot 3y ago
    Sure but that's never mentioned... this is always talked about as common sense "this is how you make sure your battery doesn't die." It seems as though problems with parasitic drain are so common that this has become standard advice?
Dave_Rosenthal 3y ago
I think a cheap thermal camera would be very helpful in these situations with a relatively fast drain. A car battery is ~1 kWh so anything that drains it in a few days is dissipating on the order of 10 watts. In my experience that's very easy to see in a thermal camera. Just leave the car in a nice thermally-stable place for a day and then go hunting.
mattbrewsbytes 3y ago
Imagine as a software developer you tracked your time working tickets, your pay was hourly, and depending on the ticket type you were prescribed how long that ticket should take and paid those set hours whether you went over/under the set hours. This sounds completely insane but this is how car mechanics work (as I understand a lot of shops do this). Replacing a battery might be 1/4 hour labor, replacing brakes on car model XYZ is 1.25 hours, etc. This is why mechanics won't really want to spend time on issues like this. It could be a wild goose chase tracking down every electrical sub-system in the car only to find something chewed thru a wire somewhere under a panel. The fix might be $15 in parts and 20 hours of actual labor but their system might quote replacing a wire as 1 hour labor.
- winrid 3y ago
  That's kind of how dealer mechanics work but not any other mechanic... They work for 10 hours, you get billed for 10 hours.
  - jonfw 3y ago
    Many shops work by book time, not just dealers, although obviously YMMV based on the shop and the work. It’s more common for routine maintenance to be charged by book time since it’s a standard procedure, less common for more complicated issues
  - c4mpute 3y ago
    > That's kind of how dealer mechanics work Refinement: That's kind of how dealer mechanics work when they know that book time they are billing is more than the time they actually need for the task. For all the other situations, there is book time like "diagnosis, complexity high, diagnostic equipment involved" billed per 6min unit.
pengaru 3y ago
> 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. Having worked as a mechanic in my youth, and worked as a software engineer in SV, the kinds of troubleshooting skills and detail-oriented attention span involved in diagnosing these issues are far more common in the latter than the former industries. My impression is it's rare for someone with such abilities to stay a mechanic, they can earn far more money in tech, with less exposure to hazards. On the subject of mechanics failing to diagnose electrical issues, I have my own story too: Decades ago, back in IL, a friend inherited a low-mileage minimalist Ford Escort hatchback, manual trans, crank windows, it was a great little econobox to inherit, on paper. He kept having the battery die on him. Not being a mechanic or even a hobbyist gearhead himself, he kept bringing it to shops. They replaced the alternator, the wiring harness, the battery, the starter, they just kept throwing parts at the car. This is what most "mechanics" do nowadays; a poorly informed process of elimination via new parts, on your dime. I hadn't been in contact with this friend for years when I heard about this "cursed" low-mileage car sitting in his garage, full of new parts with invoices totaling well over $1k. He was car-less at the time because of this situation. I offered to fix it for him, but he didn't have any confidence left in the vehicle or my ability to fix it, he was understandably fatigued by the whole thing. So I offered something like $250 and took the car off his hands. 15 minutes with a voltmeter revealed a huge voltage drop across the negative battery terminal and the chassis. Followed the negative strap to where it attached to the chassis and the area was corroded (recall it's an IL car). Removed the rusty bolt, wire-brushed the unibody steel behind it, the bolt and cable lug, slapped dielectric grease on everything and reassembled. The car charged the battery fine and ran like a champ. I ended up selling it back to him a year or two later for basically what I paid plus a few hundred for my trouble/towing etc. He wouldn't even take it back until I had driven it for years to prove it was fixed. It was that brutal an experience for him, dealing with "expert" "mechanics" bleeding him dry.
jseutter 3y ago
Eric O from the South Main Auto youtube channel has some great videos on tracking down parasitic drains on modern-ish cars. From his videos I learned that often cars won't fully sleep for up to 45 minutes depending on the model and manufacturer, as well as checking for the voltage drop across fuses to figure out which circuit is draining the battery. With this I was able to track down a parasitic drain in my 2000 Beetle (failing door lock). I'm sure he mentioned other tips as well but those are the ones that stick out to me.
bonestamp2 3y ago
> The second told me it's normal for the battery to die if you don't drive it for 3 days No, this is not normal. When the cars are manufactured, they often sit for more than 3 days just to get on a train for delivery. During transport they often sit for more than 3 days.
oliwarner 3y ago
> mechanics really don't like digging into the electrical Mechanics don't like fishing expeditions for nonessential things. $100/h for 2+ hours diagnostic, followed by tedious parts to replace and pair up. A new battery every couple of years and a trickle charger probably seems like better value to them.
dd36 3y ago
I solved one recently. Really wish there was a simple time logging multimeter that you could leave plugged in 24 hours.
- nikau 3y ago
  Most cheap multimeters have an ir or similar data port you can use for that. Just need to hold a button when turning on the meter to disable the auto power of timer, then you run software on a laptop to log the data to csv
rootsudo 3y ago
Heh, I also have an NC2 Miata, and I don't drive it for 3-6 month periods, and it still starts on the first/second engine spin. If the battery is over 3 years old, I would replace it and start anew simply because of the life/abuse it'd had so far. And then I'd start at the obvious ones - radio, aftermarket radio, alarm, etc. You can literally put a multimeter along the fusebox to see what is pulling voltage after - but most likely it will be something along 12V connected switch. Wiring isn't problematic, but if you have a hitch installed it may be wired to always be on.
lukevp 3y ago
I also have a parasitic draw on my NC Miata, and ALSO use a battery tender every time I park it! If you find out the issue, let me know, would be interesting to see if it’s the same!
aivisol 3y ago
For my VW van it was alternator - one of the diodes in the rectifier was obviously blown and leaked current backwards.
xeromal 3y ago
I'm sure if the mechanic was paid for it hourly they'd gladly tear your car apart trying to find the drain, but I think most people can't stomach that. If anyone takes a car to a mechanic and asks for the estimate and the estimate is (100$ an hour until I find the leak and it may take a whole day or two), then most people are gonna gag. You need to find an expert in your car.
iKlsR 3y ago
For me it lasted close to 4 years. I had installed a tracker that uses a SIM that you have to keep topped up to receive the messages. No issues where I live so over time I stopped and didn't even think about it. Fast forward, I went through 3 batteries, couple mechanics, bought a portable jumper and a physical battery disconnector and even got a voltage meter and was mucking around with the fuse box etc and just grew to live with it until one day I was cleaning the car, saw the thing and just disconnected it and then a few weeks later I noticed that leaving the car on weekends the battery was fine the Monday (usually had to jumpstart as it would drain). Turns out the tracker was trying to send messages almost every minute THAT it couldn't send messages! So it had been doing that for years and was the tiny leech on the battery, not large enough to be detected but enough to slowly drain a brand new battery over the course of a few days.
bouke 3y ago
I once had a parasitic drain on my BMW 3-series (e46). The dealership diagnosed the problem appropriately. It turned out to be the GROM Audio module I installed to replace the CD changer. It would drain the battery in about a week. So back to burning CDs and the issue was resolved.
falseeq 3y ago
[dead]

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?

stocknoob 3y ago
Or disconnect the battery (you’ll have to reset the clock, etc., which is annoying).
- ChuckNorris89 3y ago
  Not great advice. Most new-ish cars also store the dinamic engine calibration data in ECU RAM so if you disconnect the battery you can find your engine running harsher next time. So are the values of the headlights auto leveling system and other stuff. You're also risking to reset the radio/media unit security code (on cars that aren't too new but also not super old), which if you got the car second hand and the former owner didn't save the piece of paper it came with and give it to you, tough luck unlocking it.
  - stocknoob 3y ago
    Not ideal to cut power to the entire car, but that happens anyway on every battery swap, no? If you want to get fancy you can isolate the exact fuse and switch just that: https://www.ebay.com/itm/175668177479 https://www.ebay.com/itm/175668177479 Thinking more, given how common parasitic drains are, carmakers should have all non-essential fuses in a separate subpanel section that can be easily switched off/diagnosed.
    - BenjiWiebe 3y ago
      No. Good automotive mechanics plug a little 12v power supply into the OBD port before replacing the battery, to keep the ECU/radio RAM powered.
  - pvaldes 3y ago
    There are systems that can be attached to save the parameters from the car before you disconnect the battery or even to provide electricity to the car while the battery is being checked in another room. Not common to find and most people don't need them, but they exist.
3y ago

peteradio 3y ago

Mechanics are like doctors: find a good one and be grateful.

rozap 3y ago

It's fairly straightforward if the car is unmodified, as everything should be fused. Multi-meter between positive terminal and positive lead and pulling each fuse to see when the drop goes away will isolate the circuit. Then you've narrowed it down pretty far and can go from there. The horrible thing is if the car is modified, and you discover an un-fused circuit.

sokoloff 3y ago
I’ve had unknown draws before and many times they’re not constant draws. A constant draw is easy and quick to find. A draw that only happens when some module or other wakes up is a lot harder to find.
- flibbityflob 3y ago
  As an example, my 2017 Corolla runs the fuel pump for a while 5 hours after shutdown to test fuel system pressurization. I didn’t even know until I recently started parking it inside and I finally heard it running.
  - Arrath 3y ago
    I had to sleep in a work truck once and every hour or so it would modulate the shutters in the air vents to refresh the air in the cab or something. The click and buzz whir kept waking me up, it was quite annoying.
  - rootusrootus 3y ago
    Yeah that's pretty normal across different manufacturers, and you only hear it if you park in a quiet garage and happen to be in the garage at the moment it turns on to do it's thing. It's testing the seal of the fuel cap to make sure you aren't just venting gasoline fumes.
    - Scoundreller 3y ago
      And usually it only runs in a certain temperature range. Winter climate cars may get several months between a test.

fxtentacle 3y ago

Wow. My German car handles being parked for 3 months just fine.

rootusrootus 3y ago
So does my American car.
- EricE 3y ago
  And all three of my Japanese cars too. Definitely not normal behavior.

kybernetyk 3y ago

>It seems like mechanics really don't like digging into the electrical part of the car. If you've ever seen a car's complete wiring harness you'll know why. It's not only because there's three gazillions of wires - they're also heavily insulated with tape that makes it a nightmare to access those wires in the first place.

dylan604 3y ago
>there's three gazillions of wires My old math teacher would deduct points for not listing the units.
- airstrike 3y ago
  Numbers of wires
- rzzzt 3y ago
  "Number of wires" is a unitless quantity.
- cloudripper 3y ago
  My former English teacher would question why the age of your math teacher is relevant in this post.
  - toast0 3y ago
    Who said anything about the age of their old math teacher? You've got to learn old math and new math, presumably with different teachers.
  - dylan604 3y ago
    why are you being ageist? I have a new math teacher, therefore my previous teacher is my old math teacher.
    - vxNsr 3y ago
      Because you were being pedantic about using fake words they corrected your grammar. Former is more correct than old in this context.

lylejantzi3rd 3y ago

> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit. I can't replace it myself because it's a coded part. My mechanic won't do it because he won't confirm that's the cause. None of the other mechanics in my area have the equipment. Even the Audi dealership won't touch it because they're backed up too. So, I keep a battery jumper in the glove box and hook the battery up to a tender when I can (outdoor parking). I don't know what I'm going to do for my next car. Pretty much every car made after 2010 has coded parts and are more computer than mechanical. It does make me tempted to learn the electronics part and open a garage that focuses specifically on fixing electronic issues in modern cars.

cwillu 3y ago
If you can identify the fuse for the unit, it might be less annoying to pull it when parking rather than hooking up a charger.
- lylejantzi3rd 3y ago
  That's a great idea. I can't believe I didn't think of that. Thanks!
  - jessaustin 3y ago
    Pulling fuses is a pretty reliable way to find the relevant fuse in the first place. If the battery doesn't run down while a particular group of fuses is pulled, the one you want to pull is in that group. Start with half the fuses, then narrow down. You might have to reprogram your radio channels...
    - bityard 3y ago
      I can recommend searching for "South Main Auto parasitic draw" on YouTube. The guy is a genius at electrical troubleshooting. His strategy isn't to pull fuses, it's to set the car sit for at least 30 minutes or so (with key off) and then check each fuse with a multimeter to see which has current on it, and then check everything on that circuit. Arm yourself with schematics and wiring diagrams, otherwise it'll end up being something of a wild goose chase. (The idea being if you start pulling fuses, you can "reset" various computers in the car, which may show up as a false positive. It can take up to 30 minutes or so for all the various computers in a car to all go to sleep, although it's usually only a few minutes for most cars.)

markdoubleyou 3y ago

My last car, a 2007 Acura TSX, had the same problem--it wouldn't start after 4 or 5 days (maybe 2 or 3 during the winter). This model was from the first wave of touchscreens and bluetooth. Mechanics shrugged, pointed to the tiny, underpowered battery, and told me to drive it more. Thankfully there are a lot of car enthusiast forums out there that have been plugging away on vBulletin for years. Someone on an Acura forum had figured out that the bluetooth module was always on and looking for a connection. I tried disconnecting it, and the problem was fixed.

timlin 3y ago
Same problem and same fix for my 2009 Acura MDX.
bhauer 3y ago
Same problem with our 2007 Acura TL. And we fixed it the same way.
aksss 3y ago
God bless online car forums. Usually just awesome, well-intentioned, and helpful people that participate, with decades of knowledge indexed. There was a year way back there when the usefulness of the forums surpassed the Chilton's manual for me entirely - probably something to do with the addition of YouTube.

brewdad 3y ago

Don't ever go back to that second mechanic.

scrlk 3y ago

> It seems like mechanics really don't like digging into the electrical part of the car Probably worth taking it to an auto electrician, rather than a mechanic.

alexchantavy 3y ago

I saw this on the Gears and Gasoline Youtube channel: https://youtu.be/XgOowUWbCdk?t=628 https://youtu.be/XgOowUWbCdk?t=628 -- looks like a lot of work to trace a parasitic drain.

jeron 3y ago
If you like watching amateur YouTubers rip out their hair chasing electrical problems, I recommend checking out Tavarish and Samcrac. It turns out cheap flooded auction cars have tons of those
- toxik 3y ago
  Pine Hollow Auto Diagnostics South Main Auto Watch Wes Work musty1
  - LoganDark 3y ago
    Do you mean mustie1? I used to watch that channel all the time, super entertaining. Shows you all the cool technical bits of engine repair and maintenance without boring you to death.
    - toxik 3y ago
      I don't often have to write the channel name out, I think you may be right. I enjoy his genuine and unstressed demeanor towards the camera. Just a guy wrenching on some hardware and talking about it.
  - millzlane 3y ago
    +1 for SMA. The man clearly takes you through the troubleshooting process and his train of though.
  - weq 3y ago
    Jimmy making it work! https://www.youtube.com/@JimmyMakingitwork https://www.youtube.com/@JimmyMakingitwork lol @ Tavarish and Samcrac mentioned here, they are TV entertainers who are more concerned about drama. If you want to learn how to repair stuff, these guys are where its at ^

ilyt 3y ago

At the very least you know to which 2 mechanics you should never give your car to

bityard 3y ago

> It seems like mechanics really don't like digging into the electrical part of the car. That is certainly correct. Troubleshooting electrical issues takes a different set of skills than most mechanics are trained to deal with. Most mechanics are so busy that throwing parts at a problem is the best way to deal with issues where the cause isn't readily apparent. It's not worth their time to really dig into a difficult issue because if they spend 8 hours of shop time and try to bill that to a customer, the customer is going to just balk anyway. Better to throw a part at it, bill 1.5 hrs, send it out the door, and let the next guy deal with it. And then move on to some more profitable muffler and brake repair jobs. This is thankfully not ALL mechanics, but it certainly is a large percentage of them, IMO. (Yep, even dealerships.)

amtamt 3y ago
This sounds like a majority of software engineers (and their direct managers) asking to add more CPU and RAM, when software is slow, instead of analysing a problem. I guess mechanic's time is more valuable than parts.
- c4mpute 3y ago
  I'd phrase it like: parts have a higher profit margin...

explaininjs 3y ago

In the military, the folks tasked with Mechanical maintenance of vehicles are an entirely different branch with different training, infra, etc than those tasked with Electrical maintenance of vehicles. Perhaps we need a similar dichotomy on the civilian side.

legitimayzer 3y ago

> It seems like mechanics really don't like digging into the electrical part of the car. this is like saying that computer programmers don't like digging into the proprietary and binary blobs from other vendors. I am trying to say it's not fair to blame mechanics because even if they want to dig into the electronics, the car manufacturers take active measures to prevent 'random mechanics' from digging around. I suppose there are many rational and reasonable way to justify why this is so; probably all having some form of "because safety" and "because IP of vendors".

jerrysievert 3y ago

3 days is definitely not good for an NC. That said, mine is usually around 2 months before the battery is drained. That should give you some better expectations.

sterwill 3y ago
2006 NC owner here with a reasonably new battery. I keep it parked in an attached garage, so no extreme cold or heat. Mine will always start after leaving it for 1 month. I probably left it for 2 months at some point in the last two years, and it started, but that feels like pushing it. The next time a mechanic tells you cars can't sit for a few days without a battery drain problem, ask how people who park at the airport get home after a two-week trip.
- jerrysievert 3y ago
  my battery is in fairly good shape. when my nc was sitting for long periods (months), the old battery eventually gave out. I had to have it jumped once, then bought a li-on battery to jump it with just in case. the real key to long storage (beyond a trickle charger) is clean gas. right now, though, it only has to handle 2 weeks of sitting at most (in an attached garage).

micromacrofoot 3y ago

I've been to multiple mechanics, talked to roadside assistance people, posted in multiple forums, and talked to family about this problem with an old car of mine... and they all swore up and down that you should start a car if it sits longer than a weekend, maybe a week tops. They made me feel insane about it, it's one of those widely accepted things that's just not true most of the time.

jollyllama 3y ago
There are other reasons to do that unrelated to the electrical system of the car. You're keeping the engine and any other moving parts lubricated. You're burning fuel, so that you don't wind up with as much degraded oil.
- micromacrofoot 3y ago
  Sure but that's never mentioned... this is always talked about as common sense "this is how you make sure your battery doesn't die." It seems as though problems with parasitic drain are so common that this has become standard advice?

Dave_Rosenthal 3y ago

I think a cheap thermal camera would be very helpful in these situations with a relatively fast drain. A car battery is ~1 kWh so anything that drains it in a few days is dissipating on the order of 10 watts. In my experience that's very easy to see in a thermal camera. Just leave the car in a nice thermally-stable place for a day and then go hunting.

mattbrewsbytes 3y ago

Imagine as a software developer you tracked your time working tickets, your pay was hourly, and depending on the ticket type you were prescribed how long that ticket should take and paid those set hours whether you went over/under the set hours. This sounds completely insane but this is how car mechanics work (as I understand a lot of shops do this). Replacing a battery might be 1/4 hour labor, replacing brakes on car model XYZ is 1.25 hours, etc. This is why mechanics won't really want to spend time on issues like this. It could be a wild goose chase tracking down every electrical sub-system in the car only to find something chewed thru a wire somewhere under a panel. The fix might be $15 in parts and 20 hours of actual labor but their system might quote replacing a wire as 1 hour labor.

winrid 3y ago
That's kind of how dealer mechanics work but not any other mechanic... They work for 10 hours, you get billed for 10 hours.
- jonfw 3y ago
  Many shops work by book time, not just dealers, although obviously YMMV based on the shop and the work. It’s more common for routine maintenance to be charged by book time since it’s a standard procedure, less common for more complicated issues
- c4mpute 3y ago
  > That's kind of how dealer mechanics work Refinement: That's kind of how dealer mechanics work when they know that book time they are billing is more than the time they actually need for the task. For all the other situations, there is book time like "diagnosis, complexity high, diagnostic equipment involved" billed per 6min unit.

pengaru 3y ago

> 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. Having worked as a mechanic in my youth, and worked as a software engineer in SV, the kinds of troubleshooting skills and detail-oriented attention span involved in diagnosing these issues are far more common in the latter than the former industries. My impression is it's rare for someone with such abilities to stay a mechanic, they can earn far more money in tech, with less exposure to hazards. On the subject of mechanics failing to diagnose electrical issues, I have my own story too: Decades ago, back in IL, a friend inherited a low-mileage minimalist Ford Escort hatchback, manual trans, crank windows, it was a great little econobox to inherit, on paper. He kept having the battery die on him. Not being a mechanic or even a hobbyist gearhead himself, he kept bringing it to shops. They replaced the alternator, the wiring harness, the battery, the starter, they just kept throwing parts at the car. This is what most "mechanics" do nowadays; a poorly informed process of elimination via new parts, on your dime. I hadn't been in contact with this friend for years when I heard about this "cursed" low-mileage car sitting in his garage, full of new parts with invoices totaling well over $1k. He was car-less at the time because of this situation. I offered to fix it for him, but he didn't have any confidence left in the vehicle or my ability to fix it, he was understandably fatigued by the whole thing. So I offered something like $250 and took the car off his hands. 15 minutes with a voltmeter revealed a huge voltage drop across the negative battery terminal and the chassis. Followed the negative strap to where it attached to the chassis and the area was corroded (recall it's an IL car). Removed the rusty bolt, wire-brushed the unibody steel behind it, the bolt and cable lug, slapped dielectric grease on everything and reassembled. The car charged the battery fine and ran like a champ. I ended up selling it back to him a year or two later for basically what I paid plus a few hundred for my trouble/towing etc. He wouldn't even take it back until I had driven it for years to prove it was fixed. It was that brutal an experience for him, dealing with "expert" "mechanics" bleeding him dry.

jseutter 3y ago

Eric O from the South Main Auto youtube channel has some great videos on tracking down parasitic drains on modern-ish cars. From his videos I learned that often cars won't fully sleep for up to 45 minutes depending on the model and manufacturer, as well as checking for the voltage drop across fuses to figure out which circuit is draining the battery. With this I was able to track down a parasitic drain in my 2000 Beetle (failing door lock). I'm sure he mentioned other tips as well but those are the ones that stick out to me.

bonestamp2 3y ago

> The second told me it's normal for the battery to die if you don't drive it for 3 days No, this is not normal. When the cars are manufactured, they often sit for more than 3 days just to get on a train for delivery. During transport they often sit for more than 3 days.

oliwarner 3y ago

> mechanics really don't like digging into the electrical Mechanics don't like fishing expeditions for nonessential things. $100/h for 2+ hours diagnostic, followed by tedious parts to replace and pair up. A new battery every couple of years and a trickle charger probably seems like better value to them.

dd36 3y ago

I solved one recently. Really wish there was a simple time logging multimeter that you could leave plugged in 24 hours.

nikau 3y ago
Most cheap multimeters have an ir or similar data port you can use for that. Just need to hold a button when turning on the meter to disable the auto power of timer, then you run software on a laptop to log the data to csv

rootsudo 3y ago

Heh, I also have an NC2 Miata, and I don't drive it for 3-6 month periods, and it still starts on the first/second engine spin. If the battery is over 3 years old, I would replace it and start anew simply because of the life/abuse it'd had so far. And then I'd start at the obvious ones - radio, aftermarket radio, alarm, etc. You can literally put a multimeter along the fusebox to see what is pulling voltage after - but most likely it will be something along 12V connected switch. Wiring isn't problematic, but if you have a hitch installed it may be wired to always be on.

lukevp 3y ago

I also have a parasitic draw on my NC Miata, and ALSO use a battery tender every time I park it! If you find out the issue, let me know, would be interesting to see if it’s the same!

aivisol 3y ago

For my VW van it was alternator - one of the diodes in the rectifier was obviously blown and leaked current backwards.

xeromal 3y ago

I'm sure if the mechanic was paid for it hourly they'd gladly tear your car apart trying to find the drain, but I think most people can't stomach that. If anyone takes a car to a mechanic and asks for the estimate and the estimate is (100$ an hour until I find the leak and it may take a whole day or two), then most people are gonna gag. You need to find an expert in your car.

iKlsR 3y ago

For me it lasted close to 4 years. I had installed a tracker that uses a SIM that you have to keep topped up to receive the messages. No issues where I live so over time I stopped and didn't even think about it. Fast forward, I went through 3 batteries, couple mechanics, bought a portable jumper and a physical battery disconnector and even got a voltage meter and was mucking around with the fuse box etc and just grew to live with it until one day I was cleaning the car, saw the thing and just disconnected it and then a few weeks later I noticed that leaving the car on weekends the battery was fine the Monday (usually had to jumpstart as it would drain). Turns out the tracker was trying to send messages almost every minute THAT it couldn't send messages! So it had been doing that for years and was the tiny leech on the battery, not large enough to be detected but enough to slowly drain a brand new battery over the course of a few days.

bouke 3y ago

I once had a parasitic drain on my BMW 3-series (e46). The dealership diagnosed the problem appropriately. It turned out to be the GROM Audio module I installed to replace the CD changer. It would drain the battery in about a week. So back to burning CDs and the issue was resolved.

falseeq 3y ago

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