Lexus Hybrid Rolled on in (after nearly going up in flames).
Customer called me a little worried about their vehicle going up in flames. Something happened, wouldn't start and filled the cabin with acrid smoke, smell was bad enough to smell it from outside with the doors closed apparently.
Responded with a call out and had a chance to do some diagnostic work on the vehicle last week to see what was going on. Turns out they were right, terrible smell coming from within the vehicle (nothing in the engine bay), was much worse coming from the vents under the rear seats. Pulled the disconnect plug just to make sure nothing was going to be energised.
Scan turned up what is essentially a ground fault, looked a little deeper and found the P0AA6 code that resulted in a non start condition returned a 526 INF code too. Could still connect to the BMS and see that a few cells were showing as 0.00V. Had a quick look around the vehicle, auxiliary side was still ok, DCDC seemed ok too. Nothing could really be done until we took the rear seats out to access the battery and see what we might find.
Well now. Found evidence of an arc flash on the outside of the battery shielding. Could see it started burning the carpet, thankfully it didn't fully catch, or it might have burnt the car to the ground.
Seats removed, can see the battery pack. The exterior arc point is real close to the seat base/rail, made me wonder if it jumped the gap. Dealing with just under 300V DC, certainly able to bridge some distance. The top shielding/cover has separate ground straps though which had me puzzled as none of them show any signs of damage.
Started by double checking the state of the cover, wanted to make sure it wasn't live, no stray current found. Moved to popping open the inspection cover above the junction block to find the HV fuse blown and the underside of the cover blackened with carbon.
Checked the HV connections to see if they were live, all good there, isolated, so it looks like the disconnects/relays worked. Looks like we were safe enough to remove the upper shielding/cover and expose the inner components and battery modules.
WOW. Was not expecting this. Multiple arc flashes, multiple sections of wiring burnt up. Busbar between modules A and B was blackened with a hole melted through the underside. Evidence of large arc flashes occurring on both sides of module B, burnt wiring to the battery ECU. Module C looks like one or more of the cells has expelled some sort of material that has hardened. The area looks like it got so hot it has baked something into the surface of the stainless module frame and can't be scratched off. Whatever happened to module C, looks like it blew one of the covers off where the positive cable mounts.
Battery modules were only replaced about 3 years ago. More investigation needed but need to double up on some safety gloves first before removing the modules as I have checked and they are still live. Don't want to go lifting them out to find something exposed underneath that could arc out, want to have 3 layers. Plan is to disconnect all the HV circuits and run insulation tests to see if any results might show a ground pathway in any of the cabling, then start powering 12v circuits back on prior to making the decision about it being safe to go ahead and order a replacement battery.
Some more fault finding done, some info from the owners and they have been chasing a non start condition for over 12 months. Randomly the car just refuses to start and they have been disconnecting the auxiliary battery, waiting 20 mins and reconnecting to get car going again. Problem was becoming more frequent until this happened.
The vehicle went back to Toyota and they basically didn't want to touch it, just offering complete replacement of the battery as the modules were aftermarket. The P066A has returned multiple times in history, what I suspect was happening is the non start condition was actually the fault occurring, the current monitor was registering HV voltage within the chassis and shutdown the vehicle, refusing to allow the petrol motor to start or the HV system to enter ready mode. Disconnecting the auxiliary battery and allowing the system to discharge appears to have been resetting the system and restoring drive to the vehicle. The fault had returned dozens of times and was being reset each time until, finally, the complete failure occurred and this mess was the result.