2002: Turtle light, battery pack overheating, no error codes

Not sure how well this group is frequented anymore. I'm not mechanically inclined, and am facing a stressful situation with my 2002 Gen 1, at 163,000 miles. It's still running its original hybrid battery. The hybrid battery fan and duct were cleaned a month ago.

A week ago, I was going up two inclines in reverse, trying to back out of parking lots, when the turtle light came on, and the car completely lost power and couldn't move. There might have been another warning light, but it may have been because I tried to open the door while still in Drive instead of Park. It was late at night and I was very tired and in a panic. After turning the car off and on several times, the car was finally was able to move. The hybrid battery had dropped very low, to a narrow bar. I drove it around for a short bit to try to recharge it. I've driven short distances daily since then, without the turtle icon appearing.

Last night, exactly a week from last Tuesday, I had driven about 30 minutes, then parked the car for 90 minutes. I noticed while driving that the battery seemed to be trying to rebalance, and the battery icon had filled up to the maximum, covering the +/- indicators. There was a noise in the back while driving, which I now think might have been the battery fan, but I didn't connect the dots then. I got back to the car 90 minutes later, and turned the key to accessories, heard the normal clicks and switches up front, and then the noise in the back started up again. When I started the car, the turtle light came on. The car managed to move forward a few feet and then would not move further. Turned the engine off/on several times, still got the turtle light, and the car wouldn't move. Checked Dr Prius and got the screenshots with battery temps in the red: 122.0, 145.4, 147.2F. I flagged down some security guards, who helped me reposition the car, and I left it in the parking lot overnight and my husband came to pick me up. This morning, we had the car towed to the dealership, and there was no turtle light. I asked that they check the fan in addition to their usual diagnostic steps.

The service advisor called back this afternoon; they found no error codes stored. Fan works fine, tested on high, medium, and low with no problem. And the fan and duct looks clean. The technicians are stumped and not sure where to look next. They're letting it sit overnight and see if they can replicate it tomorrow. He's thinking it may be the first sign of battery failure, noting that there's large variation in block voltage. He's not 100% certain, but said if the battery is failing, it could continue to have intermittent problems, but not consistently. He did say there's also a chance that because I wasn't running the AC last night, that the fan could have pulled in warm cabin air from earlier in the day. I suppose that's plausible; it was cooler by the time I started my drive, but the inside of the car was still warm for a bit.

I don't run Dr Prius very often, as the Delta SOC had been consistently at 20% for the last 3 years. Last week, after the first turtle incident, it rose to 27% and then fell to 25% during a short drive. During the second turtle incident yesterday, it was 20%. The two screenshots below were taken last night, an hour apart, during which time the battery temp readings cooled down a little.

Would anyone have any insights or suggestions for the service technicians on what they should look at? Could ECU/ECMs or sensors be at fault?

I'm willing to pay for a new HV battery pack, as this one will be 21 years old come September, but I'm worried that the source of the overheating is something else and an expensive new battery pack will just be damaged if the overheating continues. Or could the overheating be from the battery constantly trying to rebalance itself because the large variation in block voltage, and be resolved with a new battery pack?

 

Version 6.8. I downloaded it a couple of years ago and never updated because it only has partial support for Gen 1.

I'm using the BAFX as well. It's a little finicky; if I switch to Torque and then switch back, I have to close out all apps and restart my phone before it'll connect.

 

The technicians won't pull the battery out. They say they're not authorized by Toyota to open the battery for inspection, as that renders the core no longer viable and thus subject to the core charge. I don't buy that, but I'm going to pick my battles and let that one go. They've had it two days and still can't find anything wrong; they'll do another test drive tomorrow but I'm not hopeful.

I agree about having gotten my money's worth. I'm more than prepared to spring for a new battery pack - have actually been saving for a couple of years in anticipation, but I'm worried that it may overheat as well if there's some other underlying issue. At some point I'm probably going to bite the bullet and replace the pack; it's just a question of when, and whether I want to go OEM (original plan) or Green Bean (considering this now so I'm not out as much $$$ if it fries)