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Engine turns ON while breaking

Discussion in 'Gen 3 Prius Technical Discussion' started by Piotrus Pan, Aug 20, 2016.

  1. Piotrus Pan

    Piotrus Pan Member

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    Hi all!
    I have this strange thing, I noticed it couple of months ago. It might have started after software update done by Toyota service.

    While I'm breaking and the battery is not full, the engine turns on for 2-3 second (revs once) and turns off if I'm still breaking after that time.
    This happens only at 70km/h (~43miles/h).
    When the battery is full and the car is breaking using the engine it also revs the engine once at that exact same speed and goes back to normal.
    Any of you have the same? Is that normal? Cause it's a little bit annoying.
     
    #1 Piotrus Pan, Aug 20, 2016
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Any time the Prius exceeds about 70 km/h, the engine has to run to prevent bearing damage to Motor/Generator1. If you brake at exactly that speed you may trip the engine until the car lowers the speed. Under some circumstances, usually involving long steep descents, the engine may run as well acting as an air pump (rotating but not using gas) If you live in a mountainous region it may be trying to slow the car that way. (if you press harder on the brakes, does the engine get faster and louder?)
     
    #2 JimboPalmer, Aug 20, 2016
  3. Piotrus Pan

    Piotrus Pan Member

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    "Any time the Prius exceeds about 70 km/h, the engine has to run to prevent bearing damage to Motor/Generator1."
    Yes, I know that but in my case when I'm going down hill 90km/h and break, the engine turns off completely. When I decelerate to 70km/h it turns on again and quickly turns off if I'm still breaking.

    "(if you press harder on the brakes, does the engine get faster and louder?)?
    Only if the battery is full but it will still rev the engine when decelerating at 70km/h.
     
    #3 Piotrus Pan, Aug 20, 2016
  4. DonDNH

    DonDNH Senior Member

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    Have you replaced your 12V battery? When it starts failing, some very strange problems have been reported.
     
    #4 DonDNH, Aug 20, 2016
  5. Piotrus Pan

    Piotrus Pan Member

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    Last year I had an issue cause it got drained, not sure how but it fell to 10,5 or something. The car started after that and I did 2500km in two days driving home and the battery showed 12,9V. I'll go check with a multimeter right now to see.
     
    #5 Piotrus Pan, Aug 20, 2016
  6. john1701a

    john1701a Prius Guru

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    If the battery is full, the engine will start.

    If the engine is being used for braking, the engine will start.

    Both are normal behaviors. That's part of the hybrid system. It knows what needs to be done to ensure longevity of the battery and to optimize for efficiency. At times, it does seem counter-intuitive those. The behavior will alter a little as the battery ages too.
     
    #6 john1701a, Aug 20, 2016
  7. Piotrus Pan

    Piotrus Pan Member

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    12,6V with car OFF, 14,3V when the car is ON. After 20 minutes the battery went to 12,9V with the car OFF.
     
    #7 Piotrus Pan, Aug 20, 2016
  8. Piotrus Pan

    Piotrus Pan Member

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    Well it's really counter intuitive. When I'm going down hill breaking and the battery is at half charge, when the speed is between 90km/h and 72km/h the engine is off, when I'm still slowing down and hit 70km/h the engine revs up and turns off.
     
    #8 Piotrus Pan, Aug 20, 2016
  9. john1701a

    john1701a Prius Guru

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    That's normal. A full battery is not... which is why the engine is revving, to consume the excess electricity. Too much shortens battery life.
     
    #9 john1701a, Aug 20, 2016
  10. DonDNH

    DonDNH Senior Member

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    12.6V after the car being shut off overnight should be OK; anything lower probably means you should be budgeting for a replacement.

    I don't recall anyone else reporting the issue you're describing. You might ask your local Toyota service manager if a similar issue has been reported and what steps they would take to correct it.
     
    #10 DonDNH, Aug 20, 2016
  11. Piotrus Pan

    Piotrus Pan Member

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    Yes, I know that too but the revving occurs also when the battery is anywhere in between full and the last 2 bars. So for example I can have 3 bars of battery and it will still rev while slowing down at 70km/h.
     
    #11 Piotrus Pan, Aug 20, 2016
  12. Piotrus Pan

    Piotrus Pan Member

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    See, the problem is that I have really shitty Toyota services near me. One wanted to change my timing belt which I don't have, one gave me an oil leak and the last one they got angry at me cause I brought my own oil (I don't have the possibility to do it myself).
    Maybe I'll try to contact someone from Toyota over internet.
     
    #12 Piotrus Pan, Aug 20, 2016
  13. CR94

    CR94 Senior Member

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    When you're braking at 90 km/hr, the engine can't "turn off completely," in the sense of stopping. Although it's not burning fuel in that circumstance, it must keep turning to avoid overspeeding one of the motor-generators.

    I've noticed the engine briefly consumes fuel when it starts turning when the car coasts from a lower speed up to a speed above about 70 km/hr on a downgrade. Then fuel flow quickly stops again (although the engine continues rotating). I assume it does that to make the transition seem a little smoother than it otherwise would feel. That's almost the opposite of the behaviour you describe, decelerating though the same speed.
     
    #13 CR94, Aug 20, 2016
  14. john1701a

    john1701a Prius Guru

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    Why do you feel there is a problem?
     
    #14 john1701a, Aug 20, 2016
  15. Piotrus Pan

    Piotrus Pan Member

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    When I decelerate and go through 70km/h, when the engine revs the whole car gets jerked forward.
    I wouldn't say my area has mountains but a lot of medium hills so I get this quite often.
     
    #15 Piotrus Pan, Aug 21, 2016
    Last edited: Aug 21, 2016
  16. bisco

    bisco cookie crumbler

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    seems odd, i don't ever recall that happening.
     
    #16 bisco, Aug 21, 2016
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