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Grinding noise when coasting, hybrid battery fully charged

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Karen in NM, Nov 22, 2024 at 7:26 PM.

  1. Karen in NM

    Karen in NM New Member

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    Location:
    Albuquerque, NM
    Vehicle:
    2020 Prius
    Model:
    Base AWD-e
    My car is a 2020 Prius AWD. I live in a mountainous area and hike a lot. When driving down a narrow mountain road (paved) where I am coasting and braking around corners, I start to hear a grinding noise when the display indicates that the hybrid battery is fully charged. The display also shows the charging arrow traveling from the front wheels to the inverter and to the hybrid battery - even when the battery is full. I have made a recording of the grinding noise and taken it to the dealer but they can't seem to figure it out. As soon as I step on the accelerator, the noise stops and of course the display shows energy transferred from the battery to the front wheels. Due to the nature of the road however, I can't accelerate very often. The dealer is unable to recreate the noise since it doesn't happen in routine city driving. Prior to having this car, I had a 2010 Prius that I bought new and drove for 150,000 trouble free miles. It was still running like new when I traded it for my current Prius. My 2010 Prius never made a grinding noise. I hope someone can help me figure this out. Thank you!
     
    #1 Karen in NM, Nov 22, 2024 at 7:26 PM
  2. FuelMiser

    FuelMiser Senior Member

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    When the traction battery is full, you are using friction braking exclusively. It could be that your rotors/pads need inspection for the grinding. Best to use B mode (engine braking) when coasting downhill to save the friction brakes. Your RPMs will soar, but this will not hurt the engine.
     
    #2 FuelMiser, Nov 23, 2024 at 11:02 AM
    BiomedO1 and ColoradoBoo like this.
  3. ColoradoBoo

    ColoradoBoo Senior Member

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    Location:
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    Vehicle:
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    Model:
    Two
    How many miles are on her, now?
    I agree, the next time you hear the grinding, shift into B and see if that helps.
    Also try to determine where the grinding is from...I'm guessing it's a brake pad, as well....probably need to get them inspected and maybe replaced and, maybe, rotors.
     
    #3 ColoradoBoo, Nov 23, 2024 at 11:23 AM
  4. BiomedO1

    BiomedO1 Senior Member

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    Model:
    LE
    ^ yes, those are great suggestions above.
    You may also want to change the ATF fluid. If the rear e-awd has a fluid sump, change that too. I've noticed that there's no change intervals for that in these cars, but they get very dirty with initial break-in. I also don't like all the foot notes and caveats in the maintenance manuals - basically lawyer's speak and get-out-of-jail-free clauses. Since your in high desert sand country - I would preemptively change it , just to see if there's some debris in there that could be the source of the grinding sound. I doubt it; but you should rule it out.

    This can also be a wheel bearing issue, but I'm assuming the 'professionals' would've/should've caught that - but you never know:confused::rolleyes:o_O:oops::sleep:
     
    #4 BiomedO1, Nov 23, 2024 at 1:54 PM
    Last edited: Nov 23, 2024 at 4:08 PM
  5. Karen in NM

    Karen in NM New Member

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    Location:
    Albuquerque, NM
    Vehicle:
    2020 Prius
    Model:
    Base AWD-e
    55,000 miles. I'm not braking too much - mainly coasting. The noise only happens once the hybrid battery is full. As soon as I step on the accelerator, the noise stops. The grinding noise seems to be more prevalent when I'm coasting. I will try shifting into B and see what happens..
     
    #5 Karen in NM, Nov 23, 2024 at 8:11 PM
  6. bisco

    bisco cookie crumbler

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    does it sound like it is coming from under the hood? can you post the recording?
     
    #6 bisco, Nov 24, 2024 at 8:28 PM
  7. kiwiscoot

    kiwiscoot Junior Member

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    Five
    could be a little stone caught in a brake on one of your hikes. The car applies the brakes lightly to slow the car down when the traction battery is fully charged. Pretty easy for a brake repair shop to check.
     
    #7 kiwiscoot, Nov 24, 2024 at 9:08 PM
  8. BiomedO1

    BiomedO1 Senior Member

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    Actually, if your just creeping along - could it be your pedestrian warning speaker?
     
    #8 BiomedO1, Nov 24, 2024 at 10:50 PM
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