Brake lock-up after switching on.

Discussion in 'Gen 3 Prius Technical Discussion' started by Currawong, Nov 26, 2013.

  1. Currawong

    Currawong Junior Member

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    Apologies in advance if this is talked about anywhere, I simply can't find anyone with an identical problem or a description of a brake issue that matches my own.

    Earlier this year I did a very hard stop to avoid an accident. The stop caused the brake lights to be locked on, such was the force I applied in my 2011 car. Toyota replace the brake light switch, but since then there has been an intermittent issue that has been impossible to invoke and continues despite the brake booster having been replaced (after I made a fuss and complained to Toyota HQ).

    It most often happened after I'd been driving then left the car parked for 10 minutes to an hour with the power off. I'd get in the car, depress the brake pedal and press the power button. When I did so, the brakes would become rock hard and, if the car was put into drive, would roll forward. The only way to stop the car would be to take my foot off the brakes and re-apply them.

    It pretty much stopped after they replaced the brake booster, but has been occurring again recently, though this time from a cold start (and annoyingly on a day when the dealer was shut). Does this describe anything known?
     
  2. Rokeby

    Rokeby Member

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    I cannot be considered an expert on either the Gen III -- I drive an '08 --
    or brake systems in general. Nonetheless I'll make a suggestion, purely
    mechanical and simplistic in nature, which may be helpful.

    Is there any possibility that your problem occurs during rainy periods?
    At such times my '08 randomly shows evidence of the disc brake pads briefly
    hanging up at start up… Its only a split second and is remedied by reapplication,
    And takes only a few feet of moment in the driveway before it is gone.

    Perhaps there is a rainwater/rotor corrosion connection for your issue.
    Am I correct in thinking there is a disc brake caliper lubricant which might
    free things up?
     
  3. Currawong

    Currawong Junior Member

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    Rokeby,

    I think I may not have described the problem adequately. What happens when I press the power button is that the brake pedal suddenly pushes back hard against my foot, making it impossible to press further. If the car is put into D then it will roll forward because the brakes aren't functioning at all. To make them function, I have to take my foot off the brake and put it back on. It is as if the brake pushes itself OFF against my foot.
     
  4. Currawong

    Currawong Junior Member

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    Excuse me for bumping this thread, but I'm guessing because I posted it around the Thanksgiving weekend that many people might have not seen it.
     
  5. jdcollins5

    jdcollins5 Senior Member

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    From what you just described it sounds like the part of the brake system that simulates the feel of a mechanical hydraulic brake system is being over pressurized. Since it was happening prior to the brake booster pump replacement it does not sound like this is the source of the problem.
     
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  6. Currawong

    Currawong Junior Member

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    Thanks jdcollins, that's very helpful. Part of the problem has been that I've had to describe this to Toyota through a translator. I need to research how the brakes work I think.

    I noticed the Scan Guage can report errors. I'm wondering if I can get one and then see if an error comes up when this happens. If I could report that it would be very helpful.
     
  7. fuzzy1

    fuzzy1 Senior Member

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    The car should be able to withstand whatever force you can apply to the brake pedal, short of bending the pedal arm, and the resulting quick stop, without damage. Some cars have had the light switch come loose and shift out of correct position, but that is not the result of pressing the pedal too hard.
    When this happens, have you put your full body weight, or at least 500 newtons / 50 kg-force / 112 pounds, into the brake pedal? If so, and you don't get useful braking effect, then this would be prima facie evidence of a problem or defect in the braking system in the U.S. At lesser pedal forces, the issue becomes murky because of legally allowed (in the U.S.) failure modes of the power brake boost.

    Other threads have expressed hints of some transient brake failure that fit much of your description, excluding the previous hard braking and the light switch issue. I even experienced it in my 2010, but no critical mass of events and clues has yet emerged.
     
  8. jdcollins5

    jdcollins5 Senior Member

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    Are you seeing the red (fault) or yellow (warning) triangle light when this happens along with any message displayed? If so then a diagnostic code has been triggered. If not then no codes are being triggered. If codes are being triggered you need to get someone to read these and post on here.

    A Scan Gauge can read standard Engine and Emission codes but not Prius Skid Control ECU codes. A custom XGauge will need to be configured to read these codes. You most likely will need to go to the dealer to have the Prius specific codes read.
     
  9. Currawong

    Currawong Junior Member

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    I have experimented with pushing as hard as I can in these situations, so I would assume that is equivalent to more than 50kgs of force, with zero effect. Literally only taking my foot off the brake and re-applying it works.

    Before the brake booster was replaced, it would happen after the car had been for a long drive then left for an hour. Now it seems to happen randomly after even short drives and being parked for 10 minutes. Ironically it happened again yesterday after having a service!



    Thanks for that info. No warning lights come up. I suspect as I have before, that the only way I would be able to record it happening would be to borrow one of their technician's computers and switch it on every time I drive to try and catch it.
     
  10. jdcollins5

    jdcollins5 Senior Member

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    One suggestion would be to capture a video of your foot on the brake and the car rolling forward. Take the video to your dealer. This has worked for other members.
     
  11. BZzap!

    BZzap! Senior Member

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    The excessive hard brake pedal would indicate a malfunction in the brake system actuator. The loss of boost to the brakes should be considered a major malfunction. Personally, I wouldn't drive the car until this issue is completely resolved. The dealer should get Toyota directly involved again.
     
  12. Currawong

    Currawong Junior Member

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    Bzzap: I agree, however, they couldn't find anything wrong, even when it was happening a few times a week. We were going to drive around the city for an hour to try and make it happen, but before we did, they decided to replace the brake booster, which fixed it...most of the time.
    I have a couple of long drives to do over the holiday period, so I'll try jd's suggestion of making a video. I can always whip out my iPhone when I start up the car and record it rolling forward in drive. I'm sure Toyota would NOT want a video of a brake malfunction online.
     
  13. BZzap!

    BZzap! Senior Member

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    My concern would be that this malfunction in the brake system might happen somewhere besides your driveway. IMHO, you shouldn't have to drive your car in a state of paranoia. I applaud the efforts of the dealer but they shouldn't have replace anything until they properly pinpointed the problem. Letting you take the car without knowing specifically that they had the problem solved is reckless. If they couldn't figuer it out, they should have called in Toyota engineers to pour over the car while you where driving around in a loaner car.
     
  14. slangenbeck

    slangenbeck Junior Member

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    How old is your starter battery? I just had mine replaced about 3 months ago, but the one they put in had a bad cell. I was experiencing a similar problem when starting my car. Brake pressure when starting the car was acting funny. I say go get that checked out and report back.
     
  15. Tideland Prius

    Tideland Prius Moderator of the North
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    I'm not sure if it's the same issue but I have noticed with the Gen 3 (and it has happened a few times but over the course of 4 years, it's not considered that often) that when you depress the brake pedal, eventually it seems that the brake booster loses its vacuum and when you start the car, the brake pedal becomes rock solid (I'm sure I made a post about it somewhere on this site when it first happened). When you try to move, the pedal essentially becomes an on/off switch so it feels like if I'm inching the car out of the spot and reapply the brakes, a slight depression ends up with a jerky stop. The only solution I've found is to release the brake pedal completely then reapply and the brake boost comes back and you can move out of the parking spot normally.

    I haven't noticed if there's a preferred scenario when it occurs (e.g. if the spot is on a slight incline vs. flat). It has happened but very infrequent.
     
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