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P300—How to diagnose if issue is ECU or HV battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by hbrubi, Jun 26, 2020.

  1. hbrubi

    hbrubi Junior Member

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    First post! 2006 Prius, 128K miles. Recently ran P0A80 and P3016 codes, battery showed signs of failure (running up and down charge while driving) and we decided to temporarily "band-aid" with a module replacement. The reason for band-aiding is because I don't live in this area, and most replacement packs here only cover a regional radius. I was hoping to drive home, and then replace if necessary.

    One module was obviously out of whack, which we replaced. First test drive after replacement went great... for 10 miles. Then all error codes from before popped up: red triangle, check engine, ((!)), VSC. Back to limp mode. But the battery charge was displaying no change onscreen: it stayed at about 3/4 full, in the blue.

    When we got home, we reopened and tested voltages. Everything was perfectly in line—range of 8.14-8.16V for all 28 modules. Took out 12V battery to do this; when we put it back in to drive to Autozone for diagnostic codes, we drove for 10 minutes beautifully again—no vacillation in battery charge—and then the same warning lights kicked on. Autozone's diagnostic equipment pulled up no codes at all. We began to think that, beyond the HV battery, there is likely a problem either with the computer, or the 12V battery, or both. Previously when my 12V started to fail, I had a blank dashboard issue (known issue for gen 2 prii, but it resolved after the 12V was replaced).

    Today I took it to the dealership which pulled up codes P3000 and P3023. They also ran voltages & resistances on the 14 blocks. Voltages ranged 16.32-16.41V. Resistance range was 0.023-0.026 ohm, with exception of block 13, which showed 0.035. I'm assuming that's why P3023 came up.

    My question: Does this variation in resistance seem confirmation enough that I should replace the whole hybrid battery pack (granting that the first codes were confirmation enough, but that I was hoping for a short-term fix, for reasons above)? Would it be wise to continue trying to test computer and/or 12V systems, to rule out those as possible causes of the P3000 code? And if so... how?
     
    #1 hbrubi, Jun 26, 2020
  2. edthefox5

    edthefox5 Senior Member

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    Welcome to a very big club. You owe us membership dues lol.

    You cant just slap in an old module that just hasn't died yet and expect the pack to last. That's called a Craigs List whack a mole repair with taillight warranty. In fact by law there business cards must have a picture of a guy with his fingers crossed and a stupid smile on his face.

    That slapped in module just hadn't died yet. It takes a tremendous amount of time to properly rebuild a g2 battery and after your done you still only have replaced modules of the same vintage that just haven't died yet. Lots of load testing. Who go's bye bye first. Find the next weak sister. Then when done balance the whole pack.

    And clean and restore all the rotten interconnect.

    Its not real common that only the ecu dies and if so it's usually because the connector is rotted out and that rot has migrated to the board.
    If that connector is rotted the whole battery is too.

    There's thousands of posts about this here use the search forums tab up top.
     
    #2 edthefox5, Jun 28, 2020
  3. ChapmanF

    ChapmanF Senior Member

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    As far as I know, P3000 is a code from the HV ECU, and all it means is "hey, the battery ECU told me something's messed up back there, go talk to it for the details" (the P3023 being those details, from the battery ECU).

    I know the fortune cookie for P3000 can say something like "abnormal signal received from battery ECU", but it isn't really "abnormal signal" as in the ECU has made smoke and forgotten how to CANBUS; it's more that the battery ECU has sent a perfectly good CAN message saying "hey there, something's abnormal back here." (Reason #473 why the fortune cookies for codes aren't as helpful as you'd hope.)

    As long as the info from the battery ECU is making sense (a block being called out, an outlier resistance consistent with that), I wouldn't invest much in the ECU being bad. Possible? I guess, but kind of at the coin-lands-on-edge level.
     
    #3 ChapmanF, Jun 28, 2020
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  4. hbrubi

    hbrubi Junior Member

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    This was really helpful—thank you.
     
    #4 hbrubi, Jul 7, 2020
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