Reversed Polarity Jump Start Damage: How to Repair?

Hello! It's my first time posting, but this is always the first website I check when I have a question about my Prius. It’s been very helpful! Yesterday I searched and read quite a few threads trying to get more ideas for solving this problem, but I still have some questions.

So, I bought a used 2001 with 60k miles on it back in summer of 2024. About 6 months later, it stopped running and was giving the red triangle. We had a friend put it on an OBD2 reader, and it gave several codes, one of which was the gas pedal. I took the gas pedal apart, and used electrical contact cleaner on it. That didn't seem to make any difference. One of the other codes led me to believe something was going on with the fuel level sensor, so I put several gallons of gas in it, and it started right up. I think it had to do with the steep sideways hill that it was parked on. Now we just make sure it’s never parked on a tilt (side to side) and the problem hasn’t come back.

Then a couple of weeks ago, I needed a jump in a parking garage about 50 miles from home. Got security to give me a jump, and noticed that they hooked up to the jump box backwards. We had my dad come up and look at it, he noticed right away that the main 100 amp fuse was popped. Got the fuse replaced, but it still wouldn't run. He got his friend to come up with an OBD2 reader, and at first it wouldn't even connect with the car. Then it wasn’t reading the VIN either. We charged the battery for a little bit, and the OBD2 reader would now connect, but it failed every test.

Towed it back home, gave it a jump start, getting all kinds of bad codes, and the battery was drawn down extremely fast, like within a couple of minutes. Took the battery out and charged it overnight, did a capacity check on the battery, which said that it was fine. Put the battery back in, started it up, the display panel was immediately much brighter, and it popped a warning that said "main battery."

We had a company (GreenTec Auto) come out to replace the main battery a few days ago, but they said that it's not the main battery. They said there were three blown fuses, which they replaced, and as soon as they attempted to turn it on, it blew the fuses again. He also said something about it giving a code indicating there was a problem with the gas pedal, again. He checked the throttle wires and harness, couldn’t find any damage there.

We decided to pull out the ECU today. Called a distributor about getting a replacement, which they said they could do, but warned us that it needs some kind of initialization process that we probably wouldn't have the tools to do. If anyone knows about that, I’d like to find out more.

The ECU numbers are 89661-47030 and 175200-5813.
The replacement has 89661-47030 and 17500-5812.

Specifically, I’m wondering if there is some way to verify whether or not the problem is the ECU? Or maybe it’s the hybrid control module? Or maybe we should just replace them both? Any other advice or ideas about what could possibly get it running again would be great.

 

Sorry about the confusion. I'm basically playing telephone with my dad about a lot of what's going on with the car.

Honestly, I don't know much about automotive anything, but he's done at home repair and maintenance for decades. Our friend that's mentioned several times in the post is also mechanically experienced and knowledgeable. Both of them have told me that they're having problems figuring it out because a hybrid has a lot of different things going on with how it's built that they aren't as familiar with, compared to a regular gasoline vehicle.

As to your question, a few reasons.
The guy from the battery replacement company said it seems like one or more of the control modules could be bad.
Various posts on this forum suggest that connecting a jump box with the polarity reversed could destroy the ECM.
It was the cheapest of the two or three that might need to be replaced. And one of the easier parts to get to.

Mainly we're really not sure how to narrow down if that's what the problem is. Hoping for suggestions for diagnosis.

Thanks again for responding.