Pumping Noise on Standby

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Priuser2016, Nov 3, 2025 at 10:54 PM.

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  1. Priuser2016

    Priuser2016 New Member

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    Hello, I'm new here, and not a lot of knowledge about cars. I'm looking to confirm what this noise could be?

    After researching I've got it narrowed down to either the Inverter Water Pump or the Coolant Control Valve. Is there any way to tell prior to going to a mechanic?

    Or I could be totally wrong and it's something else entirely since I was searching blindly. I noticed it while stopped at a traffic light. I could hear the faint noise through the front driver side seat, usually kicks in after a few minutes of driving.

    Also if it's either one of those, should I just go to the dealership or will any 3rd party mechanic be able to help out?

    The car is a 2009 Prius with about 193k miles.
    I haven't encountered any error codes yet, and Check Engine Light is OFF. The catalytic converter was replaced about 2 years ago after being stolen so I'm not sure if this is like something that happened because of that?

    Thank you so much!!


     
    #1 Priuser2016, Nov 3, 2025 at 10:54 PM
    Last edited: Nov 3, 2025 at 11:05 PM
  2. ChapmanF

    ChapmanF Senior Member

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    Yes, that washing-machine-agitator noise (or floppy-disk-seeking noise, if you remember those) is the coolant control valve. It's not very complicated to change.
     
    #2 ChapmanF, Nov 4, 2025 at 8:16 AM
  3. pasadena_commut

    pasadena_commut Senior Member

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    Not complicated but mighty inconvenient. Wiggling that odd shaped object out and back in past all the obstacles was a PITA.

    On the positive side - if that valve fails the car still works even though the CEL will be on. On the negative side - it can fail and start leaking coolant through its electrical connector, which cannot be ignored forever. So it is best to fix it.
     
    #3 pasadena_commut, Nov 4, 2025 at 1:56 PM
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