Pumping sound under driver's side dash

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by fortheanimals, Oct 31, 2013.

  1. fortheanimals

    fortheanimals Junior Member

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    For many months now, I've heard what sounds like some kind of pumping noise. This happens after starting the car and may go from brief to a few minutes. Seems to happen after every cold start and often even when warmed up. Some starts are soundless. I only recently discovered that it's coming from under the hood beneath the relay/fuse box. I can't see where it seems to be coming from.

    This doesn't seem to be affecting how it drives. Don't know if related, but I replaced the tires and noticed a 10MPG drop. I can't quite remember, but the noise and tire replacement may have begun around the same time. I had been assuming the MPG drop was related to the tires and perhaps an old 12V battery.

    Do I need to get this looked at? What is making the noise?
     
    #1 fortheanimals, Oct 31, 2013
  2. edthefox5

    edthefox5 Senior Member

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    Sounds like the brake vacuum booster. Since the Prius engine does not run all the time the brakes require a constant source of vacuum so they use an electrical pump.

    You can confirm this by pushing the brake pedal on and off a few times with the car off. This will trigger that pump so you can identify the sound.
     
    #2 edthefox5, Nov 2, 2013
  3. edthefox5

    edthefox5 Senior Member

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    Oh and your taking a mileage hit because when you bought new tires they inflate them to door placard levels.
    If you check them with a gauge you will see there around 28-30 psi.

    Inflate them to 40-38 and you'll recover your mpg.
     
    #3 edthefox5, Nov 2, 2013
  4. KhaPhoRa

    KhaPhoRa Member

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    Is this a rhythmic pumping like a "wee ooo wee ooo wee ooo wee ooo?" If it is it's likely your coolant control valve starting to fail. Mine did that for several months before finally throwing a code (p1121). I drove it like that for a couple more months and just swapped it out last week. An relatively easy job as long as you have cable operated hose clamp pliers. The part cost $70 from my local toyota dealership. If it's a steady pumping sound ignore everything I wrote :)



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    #4 KhaPhoRa, Nov 3, 2013
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