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whirring noise, both while running and after stopping

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jimsajdak, Jan 3, 2011.

  1. jimsajdak

    jimsajdak Junior Member

    Joined:
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    Location:
    berwyn
    Vehicle:
    2019 Prius
    Model:
    LE
    While driving, hear a whirring sound, happens about every ten seconds, lasting for about two...after getting home, shut off engine and this sound continued. Turned on, turned off, still continued. When off, occurs about every 20 seconds.
    Continued for the 10-15 minutes I was in the garage. Opened the engine and definitely coming from under the Synergy Hybrid box.

    Went out four hours later, and quiet. When I opened the door, sound went on again, lasting for 20-25 seconds....It then stopped and started again, occurring every 15-20 seconds, lasting for about 3 seconds

    Car's a 2008 with about 14000 on it. Have also a 2007, never had anything like this. Sounds similar to one of the noises after shut down, but thought I heard this at least once or twice before but ignored it. But today, seemed to be happening more often and then when it continued after shut down, got me worried.

    Any feedback would be appreciated!
     
    #1 jimsajdak, Jan 3, 2011
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Vehicle:
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    This sounds like the brake pressure accumulator pump. To verify, depress the brake pedal a few times to force the pump to run, and compare that noise with the noise you are hearing.

    If you confirm that this is the pump in question, then I suggest that you monitor the problem and log how frequently the pump runs after the car is IG-OFF, you have exited the car, and locked the doors. However, until you have a brake warning light come on, it is not likely that the dealer will take any action. Good luck.
     
    #2 Patrick Wong, Jan 3, 2011
  3. jimsajdak

    jimsajdak Junior Member

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    LE
    Thanks, Patrick, appreciate it very much. Have an appt on Wednesday to get it checked so will keep this (also need to get oil changed, so will also get that done while there:). Assuming they don't do anything, will defintiely monitor.

    jim

     
    #3 jimsajdak, Jan 4, 2011
  4. Lynn Goldhammer

    Lynn Goldhammer New Member

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    Location:
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    Vehicle:
    2007 Prius
    Model:
    Base
    Did you find the cause/solution? I noticed yesterday this started on my 2007 Prius. 230+k miles. My mechanic is stumped…. Perhaps a water pump?
     
    #4 Lynn Goldhammer, May 5, 2022
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    This sound could be the brake "booster" pump running. The pump pressurizes brake fluid which is stored in an "accumulator". When you step on the brake pedal, the ecu decides whether to use the friction brakes at the wheels and/or regeneration.

    If the ecu wants friction braking, is opens and closes valves to use that high pressure fluid to apply hydraulics at the wheels. As fluid is used there is less pressure in the accumulator. When it gets low enough the pump turns on again to recharge things.

    Normally once the system is pressurized it stays like that for a fairly long time- until you use the brakes. What can happen is maybe one of those valves might not seal completely, and pressure bleeds off internally all the time. So the pressure drops even when the brakes aren't being used. The pump has to run more often. Eventually the pump can get worn out and stop working. Which is not good.

    If your mechanic has a decent scantool that can get data from the ABS braking system, (or you can get a bluetooth adapter and app for your smartphone if you want to DIY - I recommend the Autel Maxi AP200) then watch the accumulator pressure sensor voltage and the pump command. I expect that the sensor voltage will drop over time down to about 3.2V, the pump will turn on (you will hear that whirring noise) and voltage will go up to about 3.6V, and the cycle will repeat.

    The only fix for this is to replace the complete ABS hydraulic assembly- it has the pump, accumulator, and valves all in one unit. It is a pricey repair. Getting a used part is a gamble. Maybe it works, maybe not. (I often say, "you already HAVE a used part, and that one is bad")

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, May 6, 2022
  6. HybridBull

    HybridBull Junior Member

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    Did you find out anything else about this noise? Have you been able to continue driving with it? My 2015 recently started doing it. Every 10 seconds.
     
    #6 HybridBull, May 12, 2022
  7. ChapmanF

    ChapmanF Senior Member

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    Every ten seconds is a well-advanced case. It should be replaced.
     
    #7 ChapmanF, May 12, 2022
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