Gen2 bricked CM, ECU, or Hybrid battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PriusOwner428, Sep 27, 2025 at 12:15 AM.

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  1. PriusOwner428

    PriusOwner428 Junior Member

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    2008 sat unattended in garage for 2 weeks.
    On return it would not start or go into ACC.
    Dash is dead. Could this be a hybrid battery gone dead?
    If it was left with 1 or 2 bars on the hybrid battery charge level, could the hybrid battery gone bad and be causing the following symptoms?

    When the power button is pressed with a working key fob inside the car nothing happens:
    No green LED on start button.
    No starting of the car.
    No going into ACC mode.
    No Ready indication.
    No display on the dash (Combination meter items like fuel gauge, odometer, gear, speedometer AND no Maint reqd, check engine, TMPS, ABS, key in car, airbag, or Triangle of death flash).

    Things that do work:
    Horn
    Headlights
    Brake lights
    Open door icon
    Internal cabin lights
    12V battery (verified good)
    +++ No key icon (when tried without key inside the car) ***
    Door lock/unlock by remote AND by buttons on door

    Other Info:
    As stated the 12V battery is good.
    Both remotes have new batteries and can lock/unluck doors, will trigger "no key" icon when try to start car without them inside the car.
    AM2 fuse is good.
    Fusible links in the engine compartment fuse box all look good.
     
    #1 PriusOwner428, Sep 27, 2025 at 12:15 AM
  2. dolj

    dolj Senior Member

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    You will need to clarify by what process you determined the 12 V battery is "good".

    Did you check that the CR2032 lithium batteries you installed in the remotes had a voltage of 3.3 V or better?

    Given all the symptoms you listed, you have a 12 V supply issue. If indeed the 12 V is "good", then you need to start checking connections and cables.
     
    #2 dolj, Sep 27, 2025 at 1:00 AM
    Brian1954 likes this.
  3. T1 Terry

    T1 Terry Active Member

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    Check the safety fuse for the hybrid traction pack, but my guess is the cell link connections have built up so much corrosion that there is a break in the series cell chain, or the battery has given up the ghost completely ....

    Can you hear the contactors close when you go to ready mode? It could be a failed contactor .....

    T1 Terry
     
    #3 T1 Terry, Sep 27, 2025 at 1:49 AM
  4. PriusOwner428

    PriusOwner428 Junior Member

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    12V was determined as good by several methods. Took it to Auto Zone for testing. Swapped it with a battery from a working 2008 Prius - the working Prius continued to work. The bricked Prius with the battery from the working Prius continued to show no signs of life.

    CR2032 in BOTH remotes are new and at 3.3V. Also both remotes remotely open and close doors. When a remote is inside the car it does NOT flash the "no key detected" warning. When there is not a remote inside the car, it does flash the "no key detected" warning. Plus physically putting the remote in the slot does not change anything.
     
    #4 PriusOwner428, Sep 27, 2025 at 2:26 AM
  5. PriusOwner428

    PriusOwner428 Junior Member

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    I guess I'm not sure what or where the "safety fuse for the hybrid traction pack" is. But if it's the fusible link in the engine compartment fuse box - it looks OK. See attached pic.

    It won't go to ready mode. When the power button is pushed there is no noise and no lights/LEDs on the dashboard.
     

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    #5 PriusOwner428, Sep 27, 2025 at 2:38 AM
  6. T1 Terry

    T1 Terry Active Member

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    Pull the plastic tray out from under the false floor in the back. Up the left hand side of the battery is an orange handle, pull it up and slide it up and the safety switch and fuse will come out. Check across the fuse using continuity on a multimeter, when you refit the safety switch, be sure to push it down after locking it into place, that closes a second safety circuit.

    T1 Terry
     
    #6 T1 Terry, Sep 27, 2025 at 5:33 AM
  7. Tombukt2

    Tombukt2 Senior Member

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    But this car is known to have the CM display issue no speedo /gas /trans . Etc ??? 3 series if clicks coming from HV battery at button press. With display issue present youay need hold button on 5 seconds . See if chk engine lite cycles . ?
     
    #7 Tombukt2, Sep 27, 2025 at 9:40 AM
  8. ChapmanF

    ChapmanF Senior Member

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    The OP has described a car where everything stays dark, even the LED on the power button, not even going to ACC.

    That's a car that's not getting 12-volt power. If the 12-volt battery was determined as good, that's fine, the power isn't getting from it to the rest of the car.

    A failed combination meter can be another cause of not powering up (though I'm not sure you lose everything, even the button LED, with that).

    Questions about the high-voltage battery are OT at this juncture. If the car is able to power up on 12 volts, it will then light the warning triangle and tell you if there's anything about the high-voltage battery that prevents going READY. No need to check that service-plug fuse, for example, unless you have the trouble code telling you to.


    Sometimes we talk about "the contactors" in back as if they were just wired directly to the power button or something, so if they don't close right away and make the car READY maybe it's their fault.

    It's not that way at all. They are controlled by an ECU in the car. The ECU closes them as one of the last steps to go READY, after everything is powered up with 12 volts and the ECU has completed a whole checklist to be sure it's OK to close them. If they don't close, you can bet it's because the ECU decided not to close them, and has set a trouble code to tell you why. (Even if one of the contactors has failed, there are trouble codes for those too.)
     
    #8 ChapmanF, Sep 27, 2025 at 10:06 AM
  9. PriusOwner428

    PriusOwner428 Junior Member

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    Where would the fuse be? It just looks a plastic orange plug. Does it have to be taken apart?
     

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    #9 PriusOwner428, Sep 27, 2025 at 10:59 AM
  10. PriusOwner428

    PriusOwner428 Junior Member

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    The CM items do not work, but neither do other display items like no Maint reqd, check engine, TMPS, ABS, key in car, airbag, or Triangle of death flash. Nothing happens on pushing the power button either visually or noise wise. The LED on the power button also never goes on. No red, amber, or green. There are just 2 or 4 clicks from the engine compartment on opening the driver side door. Probably relays.
     
    #10 PriusOwner428, Sep 27, 2025 at 11:06 AM
  11. PriusOwner428

    PriusOwner428 Junior Member

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    Well the 12V battery is getting to the following items:

    Horn
    Headlights
    Brake lights
    Open door icon
    Internal cabin lights
    12V battery (verified good)
    +++ No key icon (when tried without key inside the car) ***

    Tried using an OBDLink LX to read any error codes but it says it can not connect to the car. Even though the LEDs on the reader indicate communication happening. Can a CAN scanner read error codes from a bricked car (ie not able to go to ACC mode, ready mode etc)?
     
    #11 PriusOwner428, Sep 27, 2025 at 11:20 AM
  12. PriusOwner428

    PriusOwner428 Junior Member

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    Update: Since it looks like trying to pull it apart might break it, just put the meter across the two exposed terminals. The meter went to a solid zero. In open air the meter was showing noise of random milli ohms, but once applied to the terminals it went solid zero.
     
    #12 PriusOwner428, Sep 27, 2025 at 11:29 AM
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