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

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Patio, Jul 24, 2023.

  1. Patio

    Patio New Member

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

    Any advice is greatly appreciated. Thanks so much!! capture.jpg
     
  2. bisco

    bisco cookie crumbler

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    i would open the battery case and look for corrosion
     
  3. ChapmanF

    ChapmanF Senior Member

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    Must be a failure to communicate somewhere. P0AA6 has nothing to do with the ECM.

    It would be helpful if you could get them to tell you the three-digit "INF" subcodes that went with the P0AA6.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    That three digit code will help Do you know if they've looked inside the battery case which means they've taken the trim out of the trunk? If not it's a good idea for somebody to do that take the orange plug out and just lift the case cover look at the orange plug that goes to the ECU for the battery there's usually corroded pins in that easily correctable. Look for any white residue on the bottom of the battery tray look at the bus bar nuts and bus bars for frosting and copper that's turning black things like that you will see this readily take pictures whatever this is the kind of stuff you're looking for and you will probably see I don't even know your mileage or any of that but be prepared to see this kind of stuff going on It's about that time.
     
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    I could see it if they were talking about the battery ecu as "the ECM"

    (po-tay-to, po-tah-to)

    Posted via the PriusChat mobile app.
     
  6. ChapmanF

    ChapmanF Senior Member

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    I could see it, but I'd just correct them. The ECM is one ECU, but there are lots of ECUs that are not the ECM, and the battery ECU is an ECU that is not the ECM.

    The ECU that controls the engine is the only ECU that is also known as the Engine Control Module (ECM).

    It's not like two ways of pronouncing potato. It's like knowing potato's a nightshade, and then calling an eggplant a potato because it's also a nightshade.
     
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  7. mr_guy_mann

    mr_guy_mann Senior Member

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    Oh, I agree 100%, but if a dealer is calling it the ECM, ain't nothing I can do that'll have much affect on what they do.

    Hope for the best, plan for the worst, but don't lose any sleep because of how other folk act.

    Posted via the PriusChat mobile app.
     
  8. ChapmanF

    ChapmanF Senior Member

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  9. Patio

    Patio New Member

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    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.
     
    bisco likes this.
  10. Brian1954

    Brian1954 Active Member

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    Please make two more posts in this thread (so you will then reach 5 posts) and then add the pictures in another post after the other two posts are approved by the moderator. It would be very interesting to see the corrosion that you had.

    I am guessing that the P0AA6 trouble code will reappear in the near future.



    Posted via the PriusChat mobile app.
     
    #10 Brian1954, Jul 31, 2023
    Last edited: Jul 31, 2023
  11. Patio

    Patio New Member

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    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.
     
    #11 Patio, Aug 1, 2023
    Last edited by a moderator: Aug 1, 2023
  12. Brian1954

    Brian1954 Active Member

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    You should buy your own compatible scan tool if you want to do DIY repairs to your Prius. Take a look at the thread linked below: https://priuschat.com/index.php?threads/232741/

    Posted via the PriusChat mobile app.
     
    #12 Brian1954, Aug 1, 2023
    Last edited: Aug 2, 2023
  13. Patio

    Patio New Member

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    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.
     
  14. Patio

    Patio New Member

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

    20230806_160307.jpg

    20230806_160550.jpg
     
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  15. Patio

    Patio New Member

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

    20230806_145328.jpg

    Here's the other side:

    20230806_145058.jpg

    and again...

    20230806_145125.jpg
     
  16. Patio

    Patio New Member

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    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!
     
  17. dolj

    dolj Senior Member

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    That actually doesn't look too bad, you try to clean them up with some contact cleaner and some friction with a cloth or a popsicle stick.

    What does the mating plug look like?
     
  18. Patio

    Patio New Member

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    It looks pretty good:
    20230807_123333.jpg


    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.

    20230730_125841.jpg

    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.
     

    Attached Files:

  19. Patio

    Patio New Member

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    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.

    20230818_161345.jpg

    20230818_161708.jpg

    20230818_165116.jpg

    20230818_154943.jpg

    New cables and wires:

    20230818_165107.jpg

    20230818_192537.jpg
    20230819_161641.jpg

    20230819_161651.jpg

    20230819_161820.jpg

    20230819_184454.jpg

    20230819_162405.jpg

    20230820_123543.jpg

    20230820_123610.jpg

    20230820_123648.jpg

    Thanks for all the help, everybody!
     
  20. bisco

    bisco cookie crumbler

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    well done!
     
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