Help needed identifying hissing sound

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by JulienZ, Jul 30, 2025 at 6:59 PM.

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  1. JulienZ

    JulienZ New Member

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    Hello!

    After the BRAKE / ABS / anti-slip lights went on, the ABS module and one wheel
    Speed sensor have been replaced.

    But I just noticed this hissing sound that seems to originate from the pedals area. It comes on and off when the accelerator pedal is pressed (even very slightly like on the video) or the break pedal depressed.

    Any idea of what it is?

    Thank you!

    Julien

    —-
    2012 Prius 3
    140,000 miles
     
    #1 JulienZ, Jul 30, 2025 at 6:59 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    Some kind of air leakage apparently I would have to be doing is putting my head down they're and pushing pedal w hand . There's not a whole lot down they're . The piston that's pushed in whilst pushing with you're foot is about only thing that makes sense . Is their brake fluid in tube/s leading to brake fire wall parts ?
     
    #2 Tombukt2, Jul 31, 2025 at 7:08 AM
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  3. JulienZ

    JulienZ New Member

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    Here a better video to show the issue. The hissing sound only happens when I depress the break pedal (even when in Neutral).

    This started only after they changed the ABS module so I’m trying to understand if/how both are connected. I’ll bring it back to the shop so they can check.
    Thank you for you help!
     
    #3 JulienZ, Jul 31, 2025 at 10:23 AM
  4. Tombukt2

    Tombukt2 Senior Member

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    Lay on floor of car look up at brake pedal see the gold rod from pedal to firewall and device it pushes on . Now you know what looking at . You can now sit in car aim camera and push brake pedal slowly try n get cam close to locate hiss or maybe w head down they're you activate pedal w shoulder whilst being rt theyre
     
    #4 Tombukt2, Aug 1, 2025 at 12:25 PM
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  5. ASRDogman

    ASRDogman Senior Member

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    That is why you change BOTH at the same time!
     
    #5 ASRDogman, Aug 1, 2025 at 12:46 PM
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  6. ChapmanF

    ChapmanF Senior Member

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    Haven't played your audio, but a brief hiss associated with the brake pedal is often the sound of more/faster flow of brake fluid because of unbled air in the system.

    In a conventional brake system, you feel a softer pedal if there is air trapped. In a Prius, the pressurized fluid in the accumulator just whooshes into the line faster to squish the bubbles and reach the target pressure. But you sometimes hear it.
     
    #6 ChapmanF, Aug 1, 2025 at 1:58 PM
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  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    You better check your share settings.
     
    #7 Mendel Leisk, Aug 1, 2025 at 3:03 PM
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  8. JulienZ

    JulienZ New Member

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    Corrected, thank you!

     
    #8 JulienZ, Aug 1, 2025 at 3:33 PM
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