5 ms·

I'm not a mechanic, but I'm an amateur mechanic as far as my YouTube viewing goes, and I've never heard of this. Plenty of people I watch, get junkie, old cars,

I'm not a mechanic, but I'm an amateur mechanic as far as my YouTube viewing goes, and I've never heard of this. Plenty of people I watch, get junkie, old cars, and all kinds of things to fix but this one hasn't come up. Is it possible? I'm sure, does it happen all the time I'm somewhat suspicious.

jacquesm 3y ago
Yes, it's absolutely possible. You have a whole slew of stuff connected to that bus and if it shorts out then it can take other parties connected to the same bus with it depending on what is shorted out and how. What you think of as a taillight is actually a couple of micro computers, a DC-DC converter and a whole bunch of LEDs, connectors and so on on it's own circuit board with potentially a bunch of other IO for the safety features mentioned in TFA which could basically be anything. So all of that lives on the secondary can bus (which can have 10's of clients). Short out that bus in a creative way and you may well end up creating a nasty cascade of issues that run from one end of the car to the other. Normally this shouldn't happen. But the potential is there. In my car - fortunately - I just have regular lightbulbs. They're a pain to change out because of how the front and the back of the car are constructed but the worst they can do is blow a fuse. I keep a very small socket and driver in the car just in case I have to do that on the road because without the right tools it is impossible. And even with the tools it is a 20 minute job.
- Animats 3y ago
  > But the potential is there. Which it shouldn't be. This isn't an electric car. All you have is 12VDC. Every connection should be able to tolerate +-12VDC without damage.
  - jacquesm 3y ago
    Those taillights have their own LED drivers and not rarely they pulse the LEDs with far more than twelve volts to get them to be brighter. The pulses are super short so they don't damage the LEDs. I don't have any idea if the Ford in the article uses that trick but I've seen it on a couple of other cars as well. Usually they are simple DC/DC converters using buck-boost drivers to make the higher voltage. Moisture (tail light leak mentioned in TFA) could lead to that voltage being present on the bus (at low current, but those bus drivers are puny). https://www.ti.com/lit/ds/symlink/lp8868v-q1.pdf?ts=1701522708060&ref_url=https%253A%252F%252Fwww.ti.com%252Fpower-management%252Fled-drivers%252Fautomotive-led-drivers%252Fproducts.html https://www.ti.com/lit/ds/symlink/lp8868v-q1.pdf?ts=17015227... Datasheet of a typical driver. So 60+ V out, nice little series inductor, 6A peak current on pulses a few ns wide. That'll do it, though the best CAN bus drivers on the market could easily sustain that without damage I'm pretty sure that not all of them would and I've seen them give up the ghost in e-bikes from transients (CAN is used in e-bikes extensively, both for the main components (battery, motor, UI) as well as for auxiliaries (front and rear lights, charger). On another note: the price for the repair is ridiculous, but that's mostly because anything involving a transistor from a car brand is marked up 1,000%. Boards that don't cost more than $20 to make sell for hundreds of $, and replacing them is going to be a ton of work because of how it's all put together. A (sealed) taillight assembly could easily be $800. Headlights are usually even more expensive. In general, about Ford: great when it works. But fragile and bad engineering on plenty of parts, notably: light assemblies, various braces (including the one that holds up your transmission, don't ask me how I know about that), trim pieces and most of the interior. Engines are great, it's almost like they are designed and built by a different company. Warranty is a ridiculous back-and-forth on things that are clear manufacturing or even engineering faults and you, the customer end up in the middle (and usually pay for the privilege). I had an F150 in Canada, and I liked it from the utility perspective but the reliability wasn't there and Ford as a company utterly sucks and will never see another dime from me. 25 years ago Ford was one of the biggest brands here, today they have a negligible market share in the personal vehicle segment. https://allecijfers.nl/auto/ford/ https://allecijfers.nl/auto/ford/ Down 75% from their peak in the 80's, I would not be surprised at all if at some point they pull out of the market altogether.
    - Animats 3y ago
      > (Ford) Engines are great, it's almost like they are designed and built by a different company. They were. Ford had not only an Engine Division, but a separate V-8 Engine Division. Both were their own fiefdoms with their own management. To this day, Ford has separate self-contained engine plants. GM is divided up differently, with foundries that do hot metal work for multiple parts of the vehicle. No idea how Stellantis does things.
      - jacquesm 3y ago
        Ah, that explains quite a bit. Thank you for that bit of insight, I knew about Ford SP for the racing world and crate engines but never realized that the division ran much deeper than that. A friend of mine spooned a Ford V8 crate engine into a Midget and the result is as much fun as it is dangerous. Also the shortest clutch throw on any car I've ever seen, from fully engaged to fully free in about 1" of travel on the pedal. The firewall had to be cut out and the engine lives for a considerable portion in what used to be the interior :)
  - genter 3y ago
    The can bus can tolerate +-12VDC. Actually, something like the TJA1051T can take +-58V. The problem is that when there is a short on the can bus, you can't communicate over it. It isn't magic. I don't know what the exact problem in this case was, but I've seen it where the ABS module self destructed, and because it was on the same bus as the ECU and BCM, the BCM wasn't able to tell the ECU to start.

jacquesm 3y ago

Yes, it's absolutely possible. You have a whole slew of stuff connected to that bus and if it shorts out then it can take other parties connected to the same bus with it depending on what is shorted out and how. What you think of as a taillight is actually a couple of micro computers, a DC-DC converter and a whole bunch of LEDs, connectors and so on on it's own circuit board with potentially a bunch of other IO for the safety features mentioned in TFA which could basically be anything. So all of that lives on the secondary can bus (which can have 10's of clients). Short out that bus in a creative way and you may well end up creating a nasty cascade of issues that run from one end of the car to the other. Normally this shouldn't happen. But the potential is there. In my car - fortunately - I just have regular lightbulbs. They're a pain to change out because of how the front and the back of the car are constructed but the worst they can do is blow a fuse. I keep a very small socket and driver in the car just in case I have to do that on the road because without the right tools it is impossible. And even with the tools it is a 20 minute job.

Animats 3y ago
> But the potential is there. Which it shouldn't be. This isn't an electric car. All you have is 12VDC. Every connection should be able to tolerate +-12VDC without damage.
- jacquesm 3y ago
  Those taillights have their own LED drivers and not rarely they pulse the LEDs with far more than twelve volts to get them to be brighter. The pulses are super short so they don't damage the LEDs. I don't have any idea if the Ford in the article uses that trick but I've seen it on a couple of other cars as well. Usually they are simple DC/DC converters using buck-boost drivers to make the higher voltage. Moisture (tail light leak mentioned in TFA) could lead to that voltage being present on the bus (at low current, but those bus drivers are puny). https://www.ti.com/lit/ds/symlink/lp8868v-q1.pdf?ts=1701522708060&ref_url=https%253A%252F%252Fwww.ti.com%252Fpower-management%252Fled-drivers%252Fautomotive-led-drivers%252Fproducts.html https://www.ti.com/lit/ds/symlink/lp8868v-q1.pdf?ts=17015227... Datasheet of a typical driver. So 60+ V out, nice little series inductor, 6A peak current on pulses a few ns wide. That'll do it, though the best CAN bus drivers on the market could easily sustain that without damage I'm pretty sure that not all of them would and I've seen them give up the ghost in e-bikes from transients (CAN is used in e-bikes extensively, both for the main components (battery, motor, UI) as well as for auxiliaries (front and rear lights, charger). On another note: the price for the repair is ridiculous, but that's mostly because anything involving a transistor from a car brand is marked up 1,000%. Boards that don't cost more than $20 to make sell for hundreds of $, and replacing them is going to be a ton of work because of how it's all put together. A (sealed) taillight assembly could easily be $800. Headlights are usually even more expensive. In general, about Ford: great when it works. But fragile and bad engineering on plenty of parts, notably: light assemblies, various braces (including the one that holds up your transmission, don't ask me how I know about that), trim pieces and most of the interior. Engines are great, it's almost like they are designed and built by a different company. Warranty is a ridiculous back-and-forth on things that are clear manufacturing or even engineering faults and you, the customer end up in the middle (and usually pay for the privilege). I had an F150 in Canada, and I liked it from the utility perspective but the reliability wasn't there and Ford as a company utterly sucks and will never see another dime from me. 25 years ago Ford was one of the biggest brands here, today they have a negligible market share in the personal vehicle segment. https://allecijfers.nl/auto/ford/ https://allecijfers.nl/auto/ford/ Down 75% from their peak in the 80's, I would not be surprised at all if at some point they pull out of the market altogether.
  - Animats 3y ago
    > (Ford) Engines are great, it's almost like they are designed and built by a different company. They were. Ford had not only an Engine Division, but a separate V-8 Engine Division. Both were their own fiefdoms with their own management. To this day, Ford has separate self-contained engine plants. GM is divided up differently, with foundries that do hot metal work for multiple parts of the vehicle. No idea how Stellantis does things.
    - jacquesm 3y ago
      Ah, that explains quite a bit. Thank you for that bit of insight, I knew about Ford SP for the racing world and crate engines but never realized that the division ran much deeper than that. A friend of mine spooned a Ford V8 crate engine into a Midget and the result is as much fun as it is dangerous. Also the shortest clutch throw on any car I've ever seen, from fully engaged to fully free in about 1" of travel on the pedal. The firewall had to be cut out and the engine lives for a considerable portion in what used to be the interior :)
- genter 3y ago
  The can bus can tolerate +-12VDC. Actually, something like the TJA1051T can take +-58V. The problem is that when there is a short on the can bus, you can't communicate over it. It isn't magic. I don't know what the exact problem in this case was, but I've seen it where the ABS module self destructed, and because it was on the same bus as the ECU and BCM, the BCM wasn't able to tell the ECU to start.