Brake Pedal Hissing Sound upon stopping and holding brake

Discussion in 'Gen 3 Prius Technical Discussion' started by Sesha, Jul 10, 2020.

  1. Sesha

    Sesha Junior Member

    Joined:
    Nov 21, 2016
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    Location:
    USA
    Vehicle:
    2011 Prius
    Model:
    Three
    Hello Prius friends,

    I am having a typical problem for the last 3 months. Initially I ignored it, but slowly its getting worse that my family is getting concerned.

    When I come to a complete stop and hold the break (like a red light) there starts off a hissing sound from the brake pedal area. Its quite evident with even radio running on the back ground. Currently even when I'm in parked if i press the brake pedal it starts off a hissing noise and the electric pump (actuator I suppose) keeps on turning-on as if its trying to maintain break pressure.

    No warning /check lights on. No evident brake performance degradation, no loss/change of brake fluids.

    I took the car to 2 dealers here in Houston, both of them could hear the sound and both ran a system check using OBD and found no codes. They told me they couldn't determine where the sound comes from. I checked myself and its only in the cabin. The hissing is like some pressure venting. It's not the ABS kick back sound.

    Dealer told me that he cannot do anything until a light comes up or something breaks down in the breaking system. This is little worrisome and not assuring, as the sounds increase each week. Well I don't want to end up in a situation without any break pressure and dealer mechanic wouldn't assure that is ruled out.

    As for the car (2011), no maintenance was skipped. I'm the only driver since I have it purchased as new and now have 94K miles

    Did any of you have this issue and what is your recommendation for me.

    Please I await your feedback and advise.

    Thanks
    Sesha.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    A steady hissing sound that the pump has to repeatedly cycle to make up for doesn't have any other explanations. If it doesn't happen when your foot is off the brake, but only when on the brake, it's one of the SLR valves in the actuator not closing completely. The dealer must be thinking as long as there is no light maybe it will magically go away because summer.

    The good news is you will eventually get a light and a code. If you're in a hurry, park somewhere and hold your foot on the brake for a nice long while. Might hasten the process along.

    I am taking your word for where the hissing is coming from, as I can't hear it myself. It is a bit curious that you say only inside the cabin.

    I would get a family member to sit in the parked car and hold the brake pedal down, while you hold a mechanic's stethoscope on the brake actuator under the hood. You really should distinctly hear the hissing there too. While you're at it you can note down how often the pump is cycling on and off.

    If you don't pick up the hissing out there with the stethoscope, this really could be a false alarm, and the sound in the cabin is just something else.
     
  3. Sesha

    Sesha Junior Member

    Joined:
    Nov 21, 2016
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    Location:
    USA
    Vehicle:
    2011 Prius
    Model:
    Three
    Hi Chapman,

    Thanks for your analysis. I will try with the mechanic stethoscope. I hope the brakes are still operational when the SLR valves break down. below is the link for an the audio file where i recorded the sound from the driver's seat. sorry they didn't allow me to past the URL directly due to my experience level on this forum.

    upload_2020-7-10_23-37-27.png
    Thanks
    Sesha.
     
  4. Attila Fekete

    Attila Fekete Member

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    Apr 5, 2019
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    Location:
    Budapest, Hungary
    Vehicle:
    2012 Prius
    Model:
    N/A
    Although different Toyota, but I had similar issue. The problem was the master cylinder (?) sealing towards the firewall. As that was different car, I would definately go eith the test ChapmanF suggested.
     
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