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Quiet hum from engine when stopped

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by amkilpat, May 16, 2008.

  1. amkilpat

    amkilpat Junior Member

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    My 2005 Prius, 26,800 mi., has always become completely silent when stopping at a stop light for a few moments. Now, there is a quiet humming noise. The service manager at the dealership heard it coming from the center of the engine compartment. He said he could also hear it in a 2005 with 75,000 mi. so there's probably nothing wrong. Is this normal? Anyone else have that quiet hum?
     
    #1 amkilpat, May 16, 2008
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The inverter emits a sound whenever the car is READY.

    The inverter coolant pump runs whenever the car is IG-ON or READY, and sounds a bit like an aquarium pump.

    My guess is that you are noticing the inverter hum.
     
    #2 Patrick Wong, May 16, 2008
  3. amkilpat

    amkilpat Junior Member

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    My concern is that this noise just started after the dealer replaced the water pump a few weeks ago. It wasn't noticable before that. Why would it start now?
     
    #3 amkilpat, May 16, 2008
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Well, if the noise started immediately after a pump was replaced, then it makes sense that the new part may be causing the noise. Which pump was replaced (check your service invoice if you are unsure):
    • engine coolant pump
    • cabin heater pump
    • engine coolant heat recovery pump
    • inverter coolant pump
     
    #4 Patrick Wong, May 16, 2008
  5. amkilpat

    amkilpat Junior Member

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    The statement says "failed water pump, removed and replaced water pump, 161011 T199 T299 1.4" Under "Parts" it says Number 16290-21011, description: Pump assy, water. Hard telling what pump they replaced by this description.
     
    #5 amkilpat, May 19, 2008
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I agree that the description is not helpful. I looked up the description (PUMP ASSY, WATER W/M) in the online parts catalog of a dealer, and that doesn't shed more light. However I know that the pump in question definitely is not the engine coolant pump since I was able to see that the price for that pump is different than the pump in question.

    My guess is that the inverter coolant pump was replaced. This pump runs all the time when the car is IG-ON or READY and does make a noticeable sound when the hood is open and the gasoline engine is off.

    Since you've just started to notice the sound, maybe the new pump is noisier than the original, or maybe you had previously been oblivious to the sound. One check that you can make to ensure that the inverter coolant pump is working is to look at the fluid level of the inverter coolant reservoir. It should show a step in the fluid with the front lower than the rear, when the car is IG-ON or READY.
     
    #6 Patrick Wong, May 19, 2008
  7. hobbit

    hobbit Senior Member

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    Why does everyone keep forgetting about the throttle motor?
    The PWM going to it is frankly the loudest sound under the hood
    when the engine isn't running. The inverter pump is pretty
    quiet by comparison.
    .
    _H*
     
    #7 hobbit, May 19, 2008
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