HELP! 2005 Prius warning lights - told 2 ECUs need replaced and possibly battery assembly

Hello, I'm new here and am needing some help. I have a 2005 Prius with 162,100 miles. I bought it used in 2018 from a dealership and it only had 1 previous owner and had received all its scheduled maintenance. When I bought it I was told it had just gotten a new hybrid battery put in and it had a 3 year warranty so I thought I was safe in buying the car. (I later found out it was a refurbished HV battery put in). Exactly 1 year from buying the car (July 2019) it had to be taken in for cells to be replaced and it was covered under the warranty. Then, about 1 year from that it happened again (June 2020), I needed some cells replaced but this time they informed me it was only the parts covered by the warranty and I would have to pay over $1,000 for labor so I instead taught myself to replace the cells. It had been running fine, no decrease in gas mileage or anything, and then on 4/10/2021 I had just pulled out of my neighborhood (barely drove it 1/2 a mile) and several lights came on: the master warning light (red triangle), check engine light, brake system warning light (circle with !), and the VSC light. I turned around right away and went home. Previously, these were the lights that came on for me when I needed cells replaced so I assumed it was just that time again. On 4/13/2021 I took it to a local shop to have the codes read. When I went to drive it there, I still wasn't noticing much difference in the way it drove and this time only the master warning light and check engine light came on (previously when cells needed replaced all the lights stayed on). The codes they gave me were P3000, P0A80, C2318. Since these referred to the HV battery I assumed I was correct in my assumption of needing a few cells replaced again. Before taking it apart though I did check a few other things. I checked the inverter pump and it was fine - I saw turbulence in the fluid. I also checked the auxiliary battery and it seemed fine.

I took the HV battery out and used a multimeter to check the voltage across each cell. Now I know this isn't the correct or best way to determine if a cell is bad but I don't have a way to check them under load or discharging and this had worked for me in the past. All the cells seemed to be reading well so I was a little confused. I marked 3 that were just ever so slightly lower than the others and then hooked it back up to my car. I took it for a short drive to charge it up and then parked it and ran it while watching the screen to try and discharge it as much as possible then disconnected it and remeasured the cells. The 3 I had marked had fallen ever so slightly while the rest had stayed about the same so I went ahead and replaced those 3 because at the time I was convinced that it had to be cells that needed replaced.

It was running fine for a couple days then on 4/16/2021 the lights suddenly came back on while I was stopped at a stoplight. When the lights came on, I immediately heard the hybrid cooling fan kick on in my backseat. When the light turned green and I went to take off it had trouble. It couldn't get up to speed and engine sounded like it was revving so I pulled over into a parking lot. My dad towed it home for me the next day and I finally got a chance to look at it on 4/18/2021. I took the HV battery out again and they all read fine again. Inverter fluid still showed turbulence. I then checked the auxiliary battery once more which is when I realized the first time I checked it, I did it with the car in IGN-ON instead of ACC. So I checked it in ACC mode and it read 11.3V. So I took it out and realized it was dated as being replaced 9 years ago so I figured I had finally found the problem and replaced it. (Also what was weird though was when I took it out, there was a whole bunch of water in the frame of the car under the battery so I soaked it all up and dried it out real well before putting the new one in.)

The car drove good for about a week (little over 100 miles) but then on 4/29/2021 I was pulling into the grocery store and all the lights came back on and again heard the hybrid cooling fan come back on. I wasn't too far from home so I went ahead and drove it home but it had trouble accelerating and I couldn't really get it to go over 35 mph. I was finally able to get it into a Toyota Service shop yesterday to have them diagnose it since I've tried everything I knew to try and they gave me the DTC of P3000, P3012, P3014, and P3019. And said that I need 2 ECUs replaced: my computer assembly for the battery and the computer hybrid control. Which I'm guessing are my ECM and HV-ECU? But they said it would cost $2,300 to replace those and then after that they'll be able to take a better look at my hybrid battery that it may need a new assembly too but they won't know until the ECUs are replaced but it could cost another $3,000.

So I guess what I'm wondering is, does their diagnosis sound correct? The guy didn't sound super confident when he was explaining it to me. And if he is correct is replacing the ECUs something I could potentially do on my own? Do you have any recommended tutorials or videos for doing so? Are there any other things I should check first?

A few other side notes, I live in Ohio so my car sees all 4 seasons (sometimes all in one week) and the car hasn't been driven as much in the past 3-4 months since I'm now working from home. Any help would be much appreciated! Thanks!

 

The part numbers they gave me that they said I would need are 8989047092 and 8998147390. But you're saying it's likely a different ECU entirely? Does there happen to be a list of all the ECUs somewhere on this site? Just so I could learn more about them before digging in.

 

Thank you I will check it tomorrow and post some pictures of what I see.

 

Could this be the problem (the terminal circled in red)? And if so, what’s the best way to clean it up?

 

I tried looking at the ECU but there wasn’t anything that stuck out as wrong to me. I didn’t see corrosion on its pins.


There were several busbars and bolts though that had some bad corrosion on them so I went ahead and took them all off and cleaned them up. I hooked it all back up and it’s running fine right now but that’s usually the case until I drive it about 100 miles.

 

Well I made it to 156 miles and all the lights came back on. Any more suggestions?

 

All the same lights came back on but I have not actually read the codes again as I do not have a reader. What would be indicators that it was actually the ECUs?

 

Okay, that is just what the mechanic at the Toyota Dealership told me was wrong with my car (due to the P3000 code).

Previously when I’ve replaced modules in my car I just measured across the blocks at resting state but I know this isn’t the most accurate way of determining a bad module. But I don’t have the equipment needed to do a proper load test. Are there other options for checking the modules?

 

So what’s the easiest way to check my modules? Can it be done with general run of the mill tools I’d have on hand?

 

How would I go about getting those readings from the ECU?