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HV ECU Replacement?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Ty Wilson, Jan 23, 2014.

  1. Ty Wilson

    Ty Wilson New Member

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    Hi all. New to the forums. I have 2005 Prius with 110k. Yesterday, red triangle and check engine light came on and I lost power while driving...SCARY. Took it by dealership. They called this am and said it needed a new HV-ECU and that would cost $800. The error codes they gave me were P0A78 and P0A94. Any thoughts on this diagnosis? Anything else I should ask them to look at? I'm wondering if the HV ECU is something I could buy used and install myself? I'm not a mechanic but am comfortable with most DIY projects. Anyone know where there are some directions for this repair? Thanks so much for your help!
     
    #1 Ty Wilson, Jan 23, 2014
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I actually think it is more likely that the inverter has failed. You might ask what are the three-digit sub codes which accompany the two DTC that you listed.

    Consult techinfo.toyota.com which provides Toyota repair manual information, for more info about those two DTC and the sub codes, and also so that you can assess your ability to DIY.
     
    #2 Patrick Wong, Jan 23, 2014
  3. Ty Wilson

    Ty Wilson New Member

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    Thank you for the quick reply. I'll check into the site you mentioned. I called and got the sub codes. P0A78-306 and P0A94-588. Does that change or affirm your thoughts about the inverter?
     
    #3 Ty Wilson, Jan 23, 2014
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    P0A78-306 means there is a failure in monitoring MG2 torque, and the failed component could be either the transaxle or the inverter.
    P0A94-588 means there is a problem with the DC/DC converter within the inverter.

    So, I'm not sure how this points to the hybrid vehicle ECU which is your dealer tech's diagnosis. But at least you can see why I suggest the inverter may be the problem.
     
    #4 Patrick Wong, Jan 23, 2014
  5. Ty Wilson

    Ty Wilson New Member

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    Really appreciate your help. So for clarification are you referring to the inverter coolant pump or the bad boy "converter inverter?" I'm assuming you are pointing to the converter inverter, but just wanted to make sure.
     
    #5 Ty Wilson, Jan 23, 2014
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I am referring to the inverter which is aka "converter inverter".

    If you have a concern about the inverter coolant pump, look for fluid turbulence in the coolant reservoir when the Prius is READY. If you see this, then the pump is working OK.
     
    #6 Patrick Wong, Jan 23, 2014
  7. Ty Wilson

    Ty Wilson New Member

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    Update: So I spoke with the dealer he said the diagnosis came from a TSB EG058-06. I found a copy of that bulletin. It talks about experiencing a M.I.L. "ON" condition with the specific code P0A94/588. I have no idea if this should fix it, but they assure me it will. (I have about ZERO faith in that assurance!! Haha.)
     
    #7 Ty Wilson, Jan 23, 2014
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    OK. So back to your question about whether you can install a used hybrid vehicle ECU. Yes, you could. The ECU is hiding behind the glovebox. Consult the TSB which shows the ECU part number that you need to purchase, and techinfo for repair details. You'll need to take apart much of the front instrument panel including removing the passenger-side airbag, for access.

    autobeyours.com is usually a good source of used Prius parts.
     
    #8 Patrick Wong, Jan 23, 2014
  9. Ty Wilson

    Ty Wilson New Member

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    I'll look for specific instructions when I get home tonight. Do you know if you have to mess with programming keys when you replace this ecu?
     
    #9 Ty Wilson, Jan 23, 2014
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    No. That would be an issue if the immobilizer ECU was replaced.
     
    #10 Patrick Wong, Jan 23, 2014
  11. abboomer

    abboomer New Member

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    Ty-- what was the resolution to your problem? Did the ECU fix your symptoms? I'm having a very similar issue right now and I'm trying to diagnose before spending too much $$.

    I've detailed my symptoms here: http://priuschat.com/conversations/hows-your-prius.128921/

    Have you experienced any of these?

    Thanks, Ty.
     
    #11 abboomer, Apr 18, 2015
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