Hybrid System Issues

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by crasy169, Apr 1, 2026 at 10:40 PM.

  1. crasy169

    crasy169 Junior Member

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    I could really use some guidance for this. My wife's 2007 Prius has developed some kind of issue with the hybrid system. Initial troubleshooting was leading me to potential intermittent inverter water pump issues. Each time I checked it seemed like it was moving coolant at a good rate, but i replaced it today anyways with a genuine part from Toyota. The issue was not resolved by doing that.(Didn't think it would be.) The diagnostic software that I have is Autoenginuity and I'm sure it has its limitations. From what I can tell using the software the battery seems ok as the 14 modules all show as even and the temperatures are close to ambient temp across the three sensors. I can hear the hybrid pack fan running at high speed. The car runs and drives and reduced power.
    Screenshot of current error codes.
    Screenshot 2026-04-01 132552.png

    Previous codes before clearing.
    Screenshot 2026-04-01 124412.png

    Please let me know what other info is needed to help troubleshoot this. Hoping its not the hybrid pack or the inverter at this time.
     
    #1 crasy169, Apr 1, 2026 at 10:40 PM
  2. bisco

    bisco cookie crumbler

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    have you opened up the battery to look for corrosion?
     
    #2 bisco, Apr 2, 2026 at 8:53 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Autoenginuity is showing you the brake system codes (C1259 and C1310) that are present because of the HV ECU P3000 code, and the P3000 code is present because because of the HV Battery codes it's saying it didn't retrieve.

    Not sure if that's because the battery ECU really isn't reporting any codes, or this scan tool isn't able to see them.

    If you're sure of the scan tool (say, it's Techstream or something else definitely known to see battery ECU codes) and there's a P3000-123 with no battery ECU codes showing, then the P3000-123 troubleshooting steps go right to replacing the battery ECU.

    I'd maybe want to check for more codes with a different scan tool before going there.
     
    #3 ChapmanF, Apr 2, 2026 at 9:32 PM
    Brian1954 likes this.
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    It's been 10 years+ since I last used AutoEnginuity, but it was a fairly good "budget" pro level scan tool. If you can go into the HV battery ecu to look at data, then you SHOULD be able to retrieve any relevant codes there as well.

    That said, Chapman summed it up. The codes you have point to a fault detected by the HV battery ecu. The diagnostic procedure is to check for HV battery codes, & if there are none then replace the battery ecu.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Apr 3, 2026 at 12:26 PM
  5. pasadena_commut

    pasadena_commut Senior Member

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    Is the OP in a humid location? The corrosion getting to ECU and eating the pins there problem seems to be more common in those locations. At least that is my impression from what I read in this forum.

    In any case, checking for corrosion at the HV pack ECU connector, and inside that ECU would make sense. Buy a set of JIS bits or screwdrivers first though. When I changed the pack on our 2007 I tried to get into that ECU and couldn't open it with the Philips head bits. They are not quite the right shape, and I didn't want to risk stripping the JIS screw heads by applying more force with the wrong shape bit.

    Several threads on this issue, here is one with nice pictures:

    Corrosion/burn on Wire Frame No 2 Plug/Ecu | PriusChat
     
    #5 pasadena_commut, Apr 3, 2026 at 2:51 PM
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