'08 Prius P0AA6 hybrid battery isolation fault in battery and ecm

My '08 Prius displayed the red triangle light, amber information light, and amber VSC light as I pulled into work, but continued running fine as I parked it. Would only go into Neutral when powered back up. Later, I put an obd2 device on it and it showed no codes. After resetting error codes, the car powered up and I drove it home without issues. Next morning, same thing happened but worse: it wouldn't go into Drive even after I cleared codes. It would only go into Neutral.

Towed it to Toyota, who would only tell me "Pooaa6 hybrid isolation fault in battery and ecm" on the estimate for a whopping $5600.

I asked repeatedly if the service guy would give me subcodes. He was not very pleasant. After I insisted that he talk to the mechanic, he came back with no additional information. So I'm assuming that the mechanic used the subcodes to isolate the problem to both the battery and ecm.

However, the obd2 device showed seemingly normal battery cell voltages. See cell voltage screen capture (attached/uploaded)

Given what is now known, I have some questions:

1. Do I need the sub codes for a more accurate diagnosis?
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2. Do you think that both the ECM and hybrid battery need to be replaced?
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3. Should I replace the ECM and see if the error goes away before replacing the battery?
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4. Can you recommend a good Gen 2 ECM replacement YouTube video?
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5. Is Part # ECC11523 the correct ECM replacement?
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6. Is the Project Lithium a good quality and value replacement battery?​

Any advice is greatly appreciated. Thanks so much!!

 

Thanks @bisco! I opened the battery and the bus bars were very corroded. I cleaned up the bus bars and all error codes went away.

The two main wires/harnesses on either side of the battery had corrosion on the connectors. The corrosion appeared to extend underneath the cable sheaths. I'd like to replace them, too, but have had a very difficult time finding them online. One cable was clearly marked G9240-47020A and the other side of the battery had a pair of thick orange-sheathed wires that did not appear to have a part numbers on them. I have photos but I'm a new member so can't post links. If anyone has suggestions I'd appreciate it.

 

DOH!! The triangle of death is back and I don't want to pay another $180 to the Toyota dealership to read my code because they refuse to give me subcodes.

@Tombukt2 Unfortunately, no, they did not look inside the battery. The only information they would share with me was Pooaa6 hybrid isolation fault in battery and ecm.

I removed the battery from the car and cleaned the bus bars but I don't know what orange plug you are referring to. Is it the big orange safety plug that I pull out prior to removing the battery? I don't recall seeing pins inside it.

 

I bought the TopDon TopScan and read the codes. They are as follows:

Hybrid Control Read Codes:
P0A66 Hybrid Battery Voltage System Isolation Fault
Detail Code 1: 0
Detail Code 2: 526
Detail Code 3: 612
Detail Code 4: 0
Detail Code 5: 0
Type of ECU: HV ECU


Air Conditioner Read Codes:
B1421 Solar Sensor Circuit (Passenger Side)

I found a PDF for 526-612 but PriusChat isn't letting me post a link even though I've met all of the requirements. Here's what the PDF indicates as trouble areas:

• HV battery assembly
• Battery ECU
• System main relay
• System main resistor
• Main battery cable
• No. 2 main battery cable
• Battery plug
• No. 2 frame wire
• Junction block

I also read through a few PriusChat posts about these sub codes and they often suggest that the battery as probable culprit.

I've already replaced the bus bars, which were dirty but probably had little to do with the isolation fault issue, but I haven't removed any cells for close examination yet. I'll pull the battery out again and look for evidence of leaks and wait for a new NexCell battery that will be arriving in a few weeks.

 

I pulled the battery assembly completely apart and I think I found the culprit: a leaking cell, #14:

 

I also looked inside the ECU. I see several pins that look overheated or discolored black/purple. Do you think I should replace it?



Here's the other side:



and again...

 

Thanks, Brian, the link helped a lot! I was able to buy a reader, the TOPDON TopScan OBD2 Scanner, that gave me sub codes. Much appreciated!

 

It looks pretty good:



Nevertheless I ordered a completely new 82165-47040 Wire, Frame, No. 2 because the connectors at the other end all had blue copper corrosion on the wires.



I also bought a new G3830-47050 Plug Assembly Electric and G9242-47090 Cable, Main Battery because they both had the same blue oxidation on the ends.

 

I received the NEXcell v2 lithium upgrade pack from Dr. Prius. Installed it and my Prius runs so much better! Without even trying, I'm getting 5-10 MPG better with A/C blasting full max in 95 degree weather. The engine doesn't stop and start repeatedly at intersections. The brakes also seem to work better (perhaps because the ground fault has been removed?). Acceleration is better, especially when starting my daily commute. I've got over 100 miles on the new battery and I couldn't be happier with NEXcell!!

I replaced all of the existing cables and wires having oxidation.









New cables and wires:




















Thanks for all the help, everybody!