Door Opening "Buzz"

Discussion in 'Gen 3 Prius Technical Discussion' started by Maine Pilot, Apr 10, 2011.

  1. Maine Pilot

    Maine Pilot Active Member

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    When opening the driver's door after the car has been sitting all night, a buzzing sound from the engine compartment can be heard, lasting from 5-10 seconds. What is it?

    Yes, I've tried doing several searches, but nothing describing this noise has come up.
     
  2. Mark57

    Mark57 Active Member

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    What you are hearing is the brake pump, as it starts to build up pressure, in preparation for you to use the brakes.
     
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  3. wesayso

    wesayso Member

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    Watch the DVD that came with the owners manual.
     
  4. qbee42

    qbee42 My other car is a boat

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  5. Maine Pilot

    Maine Pilot Active Member

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    Thanks for your responses and patience.

    Tried searching for "Buzz", "Noise" and a few others, but the search function didn't give me any responses. I did view the CD that came with the vehicle, but don't remember a reference to that noise.

    Now, does opening the door actually activate the brake hydraulic pump (via a microswitch) or does it activate automatically as the pressure decreases below a certain point?
     
  6. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I'm not a technician and my explanations tend to be simplistic but it's my understanding that the Prius prepares to be driven and then shuts down when driving if finished. This is why there are noises prior to driving and noises afterwards.

    So to answer your question, it's the recognition that the driver is entering the car that initiates the preparation cycle.
     
  7. qbee42

    qbee42 My other car is a boat

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    Yes to both. Low pressure causes the pump to activate when the Prius is Ready. Opening the driver's door also enables the pump, since one of the first things drivers do is step on the brake.

    Normally the pressure bleeds off during the night, so the pump will cycle as soon as you open the door. During driving, the pump will cycle roughly every third time you brake, give or take a few.

    Tom