Is the brake pump always energized?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 8AA, Oct 30, 2005.

  1. 8AA

    8AA Active Member

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    Sometimes, when my Prius is off and locked, I hear on occasion what sounds like the brake pump running for a few seconds. This is not right after shutting down, but rather hours later. Is this a safety feature to make sure that the power brakes are always available, regardless of the state of the car? If this is normal operation, it's not suprising that the auxilliary battery can go dead in as little as two weeks.
     
  2. galaxee

    galaxee mostly benevolent

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    ah heck. my husband told me what that was but i forgot.

    i THINK it's depressurizing and repressurizing the abs system for some kind of test. i'm sure someone who remembers will post a better answer than my vague memory :huh:
     
  3. hobbit

    hobbit Senior Member

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    Yes, it's always enabled, and runs occasionally to keep pressure
    up even after the car's been off for a while. This is the reason
    that service information often says to remove both ABS MTR relays
    before working on the 12V power system with gear that can't supply
    full current to the pump motor.
    .
    There is some sort of bleed/repressurization cycle that automatically
    happens about a minute after the car is powered off. You can hear
    this as a sort of hiss, and then the pump runs for a while. After
    that it goes into the aforementioned pressure-maintenance mode.
    .
    _H*
     
  4. Frank Hudon

    Frank Hudon Senior Member

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    I do believe that after the car is shut off the brake accumulator pump is powered by the ultra capacitor pack in the back of the car and not the 12 volt aux battery.
     
  5. 8AA

    8AA Active Member

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    Thanks for the replies. When I'm showing the car to someone and the pump starts up, the person I'm with usually asked what's making that sound. I'm glad I can give them somewhat of an answer other than "I have no idea, the car has a mind of it's own"
     
  6. DanMan32

    DanMan32 Senior Member

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    I think I read somewhere that the pump stops pressurizing after so many hours of being off.
     
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