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Squeak Noise From Dash While Braking and At a Complete Stop?

Discussion in 'Gen 2 Prius Technical Discussion' started by irvadane, Aug 4, 2009.

  1. irvadane

    irvadane New Member

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    I just bought a used 2005 prius in excellent condition. When I am at a complete stop, with my foot on the brake or releasing the brake, I occasionally hear squeaky sounds coming from inside the vehicle, the dash perhaps, because you cannot hear it from the outside... I've been driving it for a week now. At first I thought it might new brakes, cause it started to go away, but now it's back again... any idea what this could be? I did not hear this sound when I test drove the car...
     
    #1 irvadane, Aug 4, 2009
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    While the Prius is READY and you are stopped, repeatedly depress the brake pedal to see if you can make the sound happen. If yes, this sound is produced by the brake pressure accumulator pump and is normal. The pump will run after the brake pedal is depressed three or four times.

    This pump is found on Prius and other Toyota hybrids. A normal car has power brake assist provided via a vacuum diaphragm mechanism that depends upon engine vacuum. Since the Toyota hybrid gasoline engine does not run much of the time, the braking system cannot rely upon the presence of engine vacuum, and the electrically-operated brake pressure accumulator pump provides the power assist function instead.
     
    #2 Patrick Wong, Aug 5, 2009
  3. jdenenberg

    jdenenberg EE Professor

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    This is the famous "chirp". It is due to air bubbles in the hydraulic fluid as they go through small ports in the "Brake Actuator". There is a TSB (BR001-07) on this problem, but bleeding the brake fluid (requires computer tools, generally at a dealer) often eliminates the chirp (it worked on my 2004).

    JeffD
     
    #3 jdenenberg, Aug 5, 2009
  4. ny biker

    ny biker Member

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    Is this "chirp" the same noise that some owners describe as a "bark"? I started hearing a noise while braking over the past winter which I thought might be the barking sound that I had read about previously.
     
    #4 ny biker, Aug 5, 2009
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