Disappearing code and lights - can I trust it?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by fmerkel, Jul 3, 2018.

  1. fmerkel

    fmerkel Member

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    This is an evolutionary new thread off another I posted about a week ago. If you want more of that tortured story:
    Sudden loss of hybrid system while driving

    In a nutshell:

    2015 Prius 4 with ~ 46k miles. No previous problems.
    Driving home from a hike. Car abruptly does a small shake, dash lights up with:
    Check engine light
    Master Warning light
    Slip indicator light
    Brake system warning light
    and of course: [Check Hybrid System......] warning in huge letters.
    Code [UO29A] pulled at home with Android app and OBD2 (can't get my Techstream to work).
    Unable to erase DTC code.

    Next day, dash lights gone. Car runs fine.
    5 miles later, new dash lights...but hybrid system works.
    Same code, only code. This time able to erase code.

    Next day take to previous owner house, he has Techstrream > NOTHING! Runs fine over there, and back.
    Short drive the next day > fine.
    Longer driver the next day > fine.

    Willing to driver it around town, not long distance or much freeway.
    See no point taking it to the dealer with no codes.

    What do you do with a 'self healing' Prius? It would be one thing if it was a nuisance problem but this car doesn't run worth a damn when the hybrid system is off line.

    My trust is seriously dented.
     
    #1 fmerkel, Jul 3, 2018
  2. ericbecky

    ericbecky Hybrid Battery Hero

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    Nothing self heals.

    Using your app, when you power up in accessory mode, what voltage is your 12v battery showing?
     
    #2 ericbecky, Jul 3, 2018
  3. ericbecky

    ericbecky Hybrid Battery Hero

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    Oh wait I see you have a seosepar thread and it showed 12.26. Got it.

    I think you need to go to the dealer. Since car is under warranty.
     
    #3 ericbecky, Jul 3, 2018
  4. fmerkel

    fmerkel Member

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    Yes, one of the first things I checked, since it's one of the first thing that gets asked. Don't see how a marginal 12v battery would cause the original problem anyway. It was going down the road at probably 50mph and the hybrid system just quit, gone, kaput, AWOL.....ugh.

    I'm pretty sure it's not rats either. :) Car was garaged. Previous owner quite tidy and organized. It's on the street here, but we don't see any rats or hear about them from neighbors.

    This does seem to be 'self healing' since there is essentially nothing I've really done to make it better.
    First time I tried to erase the DTC codes, and could not.
    The next time I could, so I did do that. But, is THAT normal behavior?
    This is my first car that even HAS codes, or at least ones I can get at. Previous cars are 1991....:D
     
    #4 fmerkel, Jul 3, 2018
    Last edited: Jul 3, 2018
  5. JC91006

    JC91006 Senior Member

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    Don't erase the codes next time the lights come on. Just bring it to the dealer and let them sort it out.
     
    #5 JC91006, Jul 3, 2018
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  6. fmerkel

    fmerkel Member

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    THAT I plan to do.

    UPDATE - Finally got Techstream working. That should hex future problems. :ROFLMAO: :rolleyes:
     
    #6 fmerkel, Jul 3, 2018
    Last edited: Jul 3, 2018
    Raytheeagle and Mendel Leisk like this.
  7. Grit

    Grit Senior Member

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    The computer is always testing each sensor, temp, thermistor, and etc. through constant cycles. For example, if the fuel cap is loose and throws a code, if you get out and tighten it, the code will go away most of the time within minutes. It threw a CEL at first but the next cycle test, there's no leakage of pressure so the CEL goes off. Technically it will go away if the issue is fixed or no longer detected, but not all CELs are the same so it may stay on even if fixed, thats when you have to erase the code.
     
    #7 Grit, Jul 4, 2018
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