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Engine runs when braking

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by anonymous, Jul 28, 2016.

  1. anonymous

    anonymous Member

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    Yesterday we were on a 10 hour trip and the engine was acting oddly; when braking, the engine sounded just like the engine brake, but the MPG indicated that it was consuming fuel (engine brake doesnt consume fuel). When braking, the engine would sound, and the MPG indicator indicates fuel consumption, it would go down to 50, with the heavier braking, like when stopping... then at a certain point it would suddenly stop... kinda hard to explain
    It seemed to happen most times but not always.
    This issue didn't happen before.
     
    #1 anonymous, Jul 28, 2016
  2. bisco

    bisco cookie crumbler

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    what was the battery icon doing?
     
    #2 bisco, Jul 28, 2016
  3. CR94

    CR94 Senior Member

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    Was it hot?
     
    #3 CR94, Jul 28, 2016
  4. bisco

    bisco cookie crumbler

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    how is your 12v health?
     
    #4 bisco, Jul 28, 2016
  5. anonymous

    anonymous Member

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    The battery wasn't full each time I noticed it happening; battery was like 4/5 or something like that. Or do you mean the red battery warning light? No red lights or warnings of any kind showed.
    It was hot at the beginning of the trip (100˚+) but later it was cooler (probably 70-80) and I think it happened that time too...
     
    #5 anonymous, Jul 29, 2016
  6. anonymous

    anonymous Member

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    I don't know; how do I know?
     
    #6 anonymous, Jul 29, 2016
  7. Raytheeagle

    Raytheeagle Senior Member

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    You will need a voltmeter and your owners manual.
     
    #7 Raytheeagle, Jul 29, 2016
  8. Raytheeagle

    Raytheeagle Senior Member

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    Hook the leads of the voltmeter up like you would to jump start the car and you will get a voltage. The owners manual tells you the locations under the hood.
     
    #8 Raytheeagle, Jul 29, 2016
  9. The Critic

    The Critic Resident Critic

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    I have had this happen to me several times too. No pattern of conditions where I can duplicate the issue. My 12v battery is fairly new so I doubt that is the issue.
     
    #9 The Critic, Aug 1, 2016
  10. anonymous

    anonymous Member

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    Update Jan/Feb 2019 for anyone finding this thread via search: I believe this issue was caused by a vacuum leak caused by the EVAP purge valve randomly binding and being stuck open, as I diagnosed in this thread. The solution is to replace the EVAP purge valve.
     
    #10 anonymous, Oct 25, 2019
    SFO likes this.
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