HV Isolation Fault (614) after head gasket

Just had my head gasket done at 300,000km. Had the work done at the shop used by the local taxi company, figuring they do more significant work on old high-mileage Priuses than anyone else around here. On my way home from the shop, it threw the exclamation mark and "Hybrid System Fault" message. Took it back in, and the shop scanned it as P0AA6, subcode 614. That means "high voltage ground isolation fault" and the 614 means it's in the inverter subsystem or its cables.

The shop says that (a) they didn't touch anything on the hybrid side in any case, they didn't even need to disconnect it to swap out the head, and (b) they checked the cables and they're nice and tight, and (c) they are going to swap in a known-good inverter to see if that corrects things, because in their experience that's what the code means 99% of the time.

I *did* start it up 3-4 times after the head gasket blew, so I suppose it's possible that the misfire vibration shook the inverter around. But it just feels like too much of a coincidence to me.

How would you approach this with the shop?

 

Good thought, thanks! However, it was only 3 days while the head was at the machine shop. Furthermore, they claim they ran it for a few hours yesterday after the head was reinstalled, and one of the mechanics took it home for the night last night to give it a shakedown cruise. I'd have thought that would have either reblanced the pack or thrown the fault. It seems super weird that I suddenly had an issue on the way home with if it had all that runtime yesterday.

 

Thanks all! The shop kept it four more days, went through the entire diagnostic checklist twice, and says the cables and connections all check out. He swapped in a known-good inverter, double checked the air conditioner cables, and checked the battery compartment for electrolyte leaks and loose insulation. No joy. He said the only remaining thing he could think of to do was to swap in a known-good traction battery, but he didn't really believe that was the issue. In the end, he gave me the keys with sincere apologies and no charge for the diagnostic work.

As soon as I started the car, the driver's window rolled down three inches and stopped. I could put it back up, but it would immediately roll itself back down. For lack of any better ideas, I used my OBD scanner to clear the fault, and started driving home. 5 minutes later, the window started behaving itself. Also, the fault did not reappear in the remaining 10 minutes to drive home. So I guess that's good.

I have no idea what's going on, so I guess I'll drive it for a few days. If the fault reappears, I'll take it to the dealer, confess to having the work done elsewhere, and beg them to re-do the diagnostic. And if the fault shuts the motor off, hopefully I can just clear it with my scanner to get off the road.

 

Not generally. I drove for 5 minutes and then cleared the fault once to see what would happen. The warning came back after about a further 15 minutes of run time, and it operates normally except for no hybrid system info available on the display. It has me wondering whether the entire fault is spurious, and there's actually a fault in what I presume are some very sensitive voltmeters that feed the computer.

Re the window: After clearing the fault, I drove 2-3 minutes more while holding the window up switch, and that's when I noticed that the window had resumed normal behaviour. We're talking like 7 minutes of total operation, so the fault clearing could be a coincidence. If I had to guess, I'd say it was more to do with battery voltage ramping up or a damp PCB warming up or something unrelated. It's just weird all these things happening at once.

Others have mentioned the AC compressor or its leads, but it's been off.

 

Note for posterity: the window thing is probably a red herring. Looks like other people have had that behaviour after an accessory battery disconnect, and it goes away after rolling the window fully up and down 3x, which I might have done inadvertently while farting around with it.