Battery ECU reporting erratic module voltages

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by NiallS, Aug 6, 2026 at 10:08 PM.

  1. NiallS

    NiallS Junior Member

    Joined:
    Nov 27, 2020
    16
    6
    4
    Location:
    Brooklyn, NY
    Vehicle:
    2005 Prius
    Model:
    Two
    Hey folks,

    Our Prius recently threw four hybrid battery fault codes (P3000, P3030, P3012 and P3013)

    Initially suspected modules 2 & 3 were failing based on P3012 & P3013. Then realized the ECU was reporting wildly erratic and physically impossible voltages for those modules. See attached chart showing modules 1 and 4 holding steady, while module 2 swings 10V to -15V, and module 3 swings +10V to 25V.

    Curious if anyone's seen this kind of fault before? My guess is the harness is corroded at the connector or module and/or the battery ECU is failing. Planning to open it up tomorrow to inspect.

    Thanks,

    Niall
     

    Attached Files:

    #1 NiallS, Aug 6, 2026 at 10:08 PM
    Last edited: Aug 6, 2026 at 10:18 PM
  2. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    8,645
    4,395
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2007 Prius
    Model:
    N/A
    I think you're on the right track, and I would be leaning toward corrosion in the sensing wires of the No 2 Frame Wire causing a break in one or more of the wires. I would replace the No 2 Frame Wire if this was the case, and if the corrosion reached the battery ECU plug, I'd clean the ECU pins or replace the ECU if the pins were too damaged.
     
    #2 dolj, Aug 7, 2026 at 6:53 AM
    Last edited: Aug 7, 2026 at 7:01 AM
    Brian1954 and NiallS like this.
  3. NiallS

    NiallS Junior Member

    Joined:
    Nov 27, 2020
    16
    6
    4
    Location:
    Brooklyn, NY
    Vehicle:
    2005 Prius
    Model:
    Two
    [mention]dolj [/mention] Thanks so much, good to know I am probably on the right track.

    ( If any members near Chevy Chase MD happen to have a used sensing harness or battery ECU for sale please shoot me a DM or reply here!)


    iPhone ?
     
    #3 NiallS, Aug 7, 2026 at 9:49 AM
  4. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    8,645
    4,395
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2007 Prius
    Model:
    N/A
    A new replacement harness is available from ACENBAY for $85: Toyota Prius Hybrid Battery Wire Harness Assembly.

    Used ECUs are readily available from wreckers or eBay.
     
    #4 dolj, Aug 7, 2026 at 9:52 AM
    Last edited: Aug 7, 2026 at 9:58 AM
  5. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    8,645
    4,395
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2007 Prius
    Model:
    N/A
    @NiallS, try using the @ in front of a user's to 'mention'.
     
    #5 dolj, Aug 7, 2026 at 9:55 AM
(You must log in or sign up to post here.)