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Prius moves a foot after shifting without releasing the brake.

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by dragonslayer8228, May 7, 2014.

  1. dragonslayer8228

    dragonslayer8228 Junior Member

    Joined:
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    Location:
    Herndon VA
    Vehicle:
    2010 Prius
    Model:
    III
    I tried hunting for other people who mentioned this in other threads but had no luck. In the last couple of months I have noticed my '10 Prius III begins to roll forward or backwards about a foot depending upon which drive mode I select without releasing the brake. So here's the normal scenario I get in the car have my foot on the brake, turn it on wait for the ready beep/light, my foot has never left the brake or lessened pressure but not so much as to trigger the hill assist, I shift into D to go forward but say a car is coming and I don't want to go yet my car moves about a foot forward and I feel the brake pump up and then resist my foot. The same thing happens if I put it in R she rolls back a foot and stops. Anyone else had this problem? I don't recall noticing it before the great ECU update but I also can't say it didn't happen before the update was accomplished.
     
    #1 dragonslayer8228, May 7, 2014
  2. HTMLSpinnr

    HTMLSpinnr Super Moderator
    Staff Member

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    Going to add a "me too" to this one. I've also had the brake booster replaced under a service campaign, and the behavior persists. It seems to be when the boost pump is still charging as you get into the car. I'd consider it a design flaw, if anything.

    You'll find that pressing harder does stop the car, but it's as if less pressure is being sent to the wheels while that boost pump is initially charging. I also find that if I release my foot and reapply, you hear a rush of pressure, and stopping effectiveness is restored.

    When I complained to the dealer, they claimed they either couldn't reproduce it, or considered it normal behavior. Had I chosen to escalate, they would have needed a regional "master technician" to come look at the problem.

    For now, it's almost habit to either be quick on the pedal to reapply, or just wait for the boost pump to finish charging before applying the pedal initially.
     
    #2 HTMLSpinnr, May 11, 2014
  3. bisco

    bisco cookie crumbler

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    Vehicle:
    2012 Prius Plug-in
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    Plug-in Base
    you gotta be quick to open the drivers door, sit down, hit the brake, hit the power button, and put it into drive all before the brake accumulator has finished.
     
    #3 bisco, May 11, 2014
    GrumpyCabbie likes this.
  4. fuzzy1

    fuzzy1 Senior Member

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    There have been several reports of various brake anomalies, but no verification or critical mass yet. Most seemed to be at startup, but some were while already in motion, and at least one resulted in a minor crash. HTMLSpinnr's version sounds closer to what I experienced in my 2010 at startup in a sloped parking lot a couple times, but I responded different so the fault path and result don't match. My 2012 hasn't experienced the same thing. But it has rolled up significantly fewer miles, hardly any of them since the ECU update, so its lack of incidents doesn't yet mean anything.

    Keep searching, but be aware that 'Search' has been having problems for a couple months, currently missing most of the posts it should find.

    If it is a matter of the power assist momentarily not working, then be aware that federal passenger car regulations regulate how the power brakes must function under a variety of different failure types. Basically, the power assist is allowed to fail, but the brakes must still work in old-fashioned manual braking mode, i.e. put your full body weight into the pedal. 118 pounds of pedal force (or 500 newtons) is a magic number in the regulations. Failure to function at that pedal force would be nearly prima facie evidence of a defect that would force a recall. But if you are not triggering the Hill Holder, you are applying much less pressure, so the defect issue (if verified) would be quite muddy.
     
    #4 fuzzy1, May 12, 2014
    prius8409 likes this.
  5. prius8409

    prius8409 New Member

    Joined:
    May 20, 2014
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    Location:
    Iowa city
    Vehicle:
    2005 Prius
    Model:
    II
    I was forced to use the emergency brakes while rolling down a ramp backwards. The car started up, but did not go into drive or brake. After calling toyota, they have been avoiding me like the plague, of course. They said my axle broke the transmission and that is why my brake isn't working. That doesn't make sense since the transmission is not responsible for the brakes and is actually part of the hydraulic system.
     
    #5 prius8409, May 23, 2014
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