Troubling sound in brake system?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by melkisadek, Mar 11, 2015.

  1. melkisadek

    melkisadek Junior Member

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    I have this light tapping sound that I don't believe is native to the otherwise healthy Prius II I'm currently driving.
    Mine is a 2007 Prius II with about 106,000 miles. The sound occurs persistently when the vehicle is ON but
    the engine is not running and the ventilation system is off. If I press down on the brake pedal I hear a light tapping similar to tappets in older cars. But since the engine is not running at this point I don't think the
    problem is there. If I let up almost all the way on the brake the noise goes away.
    I bought this car with 103,000 so I know there may be things that I need to tend to. I'm not experiencing
    any braking problems. I'd rather have some idea of what's making this sound before I check with a mechanic
    and incur a few hundred dollars of expense. I'm hoping someone here has dealt with this and can give me
    a clue.

    Thanks,
    Al
     
    #1 melkisadek, Mar 11, 2015
  2. exstudent

    exstudent Senior Member

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    Normal.

    IIRC (If I Recall Correctly), that is the accumulator pump activating, to restore the pressure that has just been used, since you stepped on the brake. This sound can be heard with the car OFF or car READY (think car has been started and engine running, but w/ the Prius, the engine may not be running due to temperature and power needs).

    You should check out What services you need and what you don't | PriusChat

    Coolant shoud have been changed at 100,000 miles. Transaxle fluid ever changed? Struts ever changed? Brakes and front caliper pins lubricated?
     
    #2 exstudent, Mar 11, 2015
  3. melkisadek

    melkisadek Junior Member

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    Thanks for the information. Since I got the vehicle with 103,000, it's quite possible the (brake?) coolant wasn't changed. The sound is constant when I'm depressing the brake and goes away when I have let
    up almost to the highest point of the brake stroke. The engine definitely isn't running and I don't think I'd
    hear anything if I had turned the vehicle off completely. I'll have to check that point out.

    Mel
     
    #3 melkisadek, Mar 13, 2015
  4. nh7o

    nh7o Off grid since 1980

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    The brake pump should run intermittently while driving normally, but it should stop running after a short time. If it runs continuously while braking, as you describe, that indicates a potential problem in the future, as it means the brake pump is having a hard time maintaining pressure in the system. At some point the ABS system will go over a threshold and show an error light on the dashboard. It may take a while, but there have been a small number of brake pump failures reported here over the years.
     
    #4 nh7o, Mar 13, 2015
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  5. melkisadek

    melkisadek Junior Member

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    This was very useful information. Will the vehicle "brain" give any kind of error report on a failing brake pump? If not, I will stay alert to the ABS error light and head for the Service Center at the slightest indication of trouble.

    Thanks,
    Mel
     
    #5 melkisadek, Mar 14, 2015
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    OP, is the light tapping sound while you're moving, or at a stop?
     
    #6 Mendel Leisk, Mar 14, 2015
  7. melkisadek

    melkisadek Junior Member

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    The light tapping sound is at a stop. As a matter of fact, I discovered that I can turn the car off and press on the brake pedal and still get the tapping sound. That leads me to guess that it's something that's electrically driven. Any suggestions?
     
    #7 melkisadek, Mar 19, 2015
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    No, but maybe it'll help someone. Interesting that it happens even with the car off. Hope you sort it out.
     
    #8 Mendel Leisk, Mar 19, 2015
  9. nh7o

    nh7o Off grid since 1980

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    Yes, the brake pump can run even with the car turned off. It can run a self test even if you don't press the brake pedal. That is why it is required to disable the ABS when doing brake work, so as to avoid popping the brake pistons out with force.
     
    #9 nh7o, Mar 20, 2015
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