EDIT: This PDF contains very detailed electrical information for the EEs who wanna go through the complaint: https://www.autoevolution.com/pdf/news_attachements/breaking-nhtsa-petition-shows-tesla-s-sudden-unintended-acceleration-is-real-and-curable-217525.pdf
Last year at /r/RealTesla, a Chinese video of a car rocketing at full speed for 1+ minutes before crashing / killing a pedestrian made the rounds. We all recognized it as one of the weirder cases of “Sudden Unintended Acceleration”, and I think that particular video really changed some minds.
While a lot of SUA events are from driver-error, it began a search into why Teslas seemed to be getting more SUA above-and-beyond the industry normal. This investigation (now filed under NHTSA) suggests that the ADC could be miscalibrated during a load-dump (or other electrical surge-like) scenario.
If the ADC associated with the accelerator pedal is off, then the Tesla will have the pedal at the wrong level of acceleration until the next calibration event, which is not going to happen until over a minute later.
This is extremely similar to that Chinese runaway Tesla, and perfectly seems to explain it. I’m glad that someone seems to have gotten to the bottom of this.
I know we talked about this on Discord but I forgot one key fact.
Tesla has an isolated 12V battery pack already. If the 12V battery pack remained isolated (for cabin / windows / sensors / etc. etc.), then all of this could have been easily avoided.
Tesla vehicles aren’t an ICE vehicle. Tesla has innately separate power supplies for power / steering (aka: the main battery pack), and a separate 12V battery pack for other purposes. This isn’t like ICE cars where the 12V line cannot be physically separated from the alternator or other aspects of the vehicle.
Ok, double comment time. So, reviewing this video: https://www.youtube.com/watch?v=rDYbvI32OBE
At 2:27 he pans across the EPAS module and the BATT1 and BATT2 connectors look exactly the same to me. They are not HVDC cables with the typical bright orange sheath, but rather just red and black. I think this is just two 12v sources. One is likely the DC/DC converter and the other is likely the battery. But for sure there’s no HV connection here and there’s no secondary battery source, it would actually just be that DC/DC converter being called “batt2”.
Odd design, but here we are. I’m positive there’s no secondary 12v source here and that it’s just feeding from “redundant” controller boards and everything feeds through the 12v battery. But I’m just open to the possibility there might be two sources on the body controllers. Again, all would be sourced from the battery and the DC/DC converter would feed through it, but that battery is in the way of all of this and is not actually redundant at all.
There’s certainly two links from BC Front to the EPAS (I keep calling it IPAS for no good reason). And they’re absolutely labeled BATT1 and BATT2. BATT1 is labeled elsewhere in the diagrams as 12v, which I presume means BATT2 means HVDC. But all of the other HV components are called out as HV in some manner, whereas the EPAS just says BATT2. I’m assuming this is tapping the HVDC power in the BC front, though.
Now, having looked at the wiring diagram, I’m wondering something about all the EPAS warning posts we’ve seen on forums over the years. It almost always seems to be related to a faulty ground or a faulty 12v battery connection somewhere, or on rare occasion a dying 12v battery. So now I’m wondering whether the EPAS controller is actually experiencing a fault because of low control circuit voltage or if there’s something else going on here. And if it’s the latter, could it manifest as low supply voltage to the DSP / ADC for the APP sensors?
Ultimately, most of these systems are fused with a FET and current sensors. So you would imagine that Tesla would have detailed logs somewhere in the system about supply voltages and current to all these peripherals. I’d love to see what that data looks like in a scenario where the EPAS warning is triggered, or on a vehicle that’s stationary but receives steering input. Certainly 1.2kW is absolutely nothing to the HV pack, but if it’s going through the same DC/DC that charges the 12v battery, it seems possible that the current could be too high and it could trigger some voltage sag. But the fact that these are all such common circuit designs, I’m just not sure I understand how it went so wrong.
The weasel words are getting to me, honestly.
A lot of the reverse-engineering / hard work seems to have come from the Youtube video, rather than the .pdf / complaint. I think I was confusing who did which work and who was making the arguments.
Fair enough, yeah. I still think the only way this gets any real traction is for a lawyer to hire an engineering team to reproduce this work on the bench and on a vehicle. I’m not sure how you do the latter safely without modifying the boards or modifying the 12v subsystem. Obviously monitoring the +12v bus is easy enough, but the impact of calibration during a low power event would have to be orchestrated carefully.