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2011 Prius shuts down when brake pedal pressed to start, but...

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Matt N, May 23, 2024.

  1. Matt N

    Matt N New Member

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    Good Day! My 2011 hybrid runs well but lately I have noticed that when I try to start the car by depressing the brake pedal, it shuts off with a click before I can press the Start button. I then hear a winding sound in the engine and after a couple of minutes the dash display lights up and the car is ready to be started. 12V battery seems to be OK - measures 14.4 when running and over the range when the car is turned off. This problem doesn't happen all the time, maybe once or twice in a day, lately. Any thoughts, please?
     
    #1 Matt N, May 23, 2024
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    What’s “it”?
    Clarify “over the range”?
     
    #2 Mendel Leisk, May 23, 2024
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  3. ChapmanF

    ChapmanF Senior Member

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    What do you mean the battery measures "over the range" when the car is turned off?

    the 14.4 when READY is no surprise; you're not measuring the battery then, you're measuring the car's DC/DC converter output.

    I suspect that when you step on the brake, the brake pressure pump is running and pulling the battery voltage down too low for the dash to light up, and you get the lights back when the pump shuts off.

    The pump normally sounds like a little rattlesnake or joy buzzer and just runs a few seconds. But at much reduced voltage, it sounds more like a dying wind-up toy and takes a lot longer to shut off.

    First guess is your 12 volt battery is ready for replacement, and if you're convinced it's a-ok, second guess is a lousy electrical connection, maybe at the battery or the nearby ground point.
     
    #3 ChapmanF, May 23, 2024
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  4. ASRDogman

    ASRDogman Senior Member

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    The 14.4 volts is from the inverter, charging the battery.
    Turn the car off, then measure the battery.
    How old is the 12v battery? If it's 5 years or older, it's likely do to be replaced.
    How much driving do you do? Around town? Highway? If you're taking short trips,
    it's likely the 12v battery is not, and has not been getting a long enough charge, and has
    slowly gotten weaker and weaker.
    You could try a 4 amp or less charger on the battery for 12 hours, that should give it a
    full charge. Then measure it. It should be up around 12.7 or so. If after charging it's only
    around 12.3 or so, likely it's life has been used up.

     
    #4 ASRDogman, May 23, 2024
  5. Tombukt2

    Tombukt2 Senior Member

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    Yeah your battery's got 12 and 14 volts respectively. It just has no AH behind that voltage Time for a 12 volt more than likely
     
    #5 Tombukt2, May 23, 2024
  6. bisco

    bisco cookie crumbler

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    my battery has been over the range for years. what's not to like?
     
    #6 bisco, May 23, 2024
  7. Matt N

    Matt N New Member

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    Thank you all for your kind replies. "It" is the dashboard display.
    Over range in my old Fluke meter is 12.3V in a different multimeter.
    I have not checked the 12V battery voltage when the brake pedal is depressed.
    I will replace the 12V battery today and get back to you with what I find out. I didn't suspect the 12V battery, which is 5-6 years old, because the low battery icon didn't light up.
     
    #7 Matt N, May 23, 2024
  8. ChapmanF

    ChapmanF Senior Member

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    ♫Home over the range
    where the vultures and bald eagles prey ♫
     
    #8 ChapmanF, May 23, 2024
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  9. ASRDogman

    ASRDogman Senior Member

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    I don't believe there is a "low battery" icon for the 12v battery.

    Don't forget to charge the new battery for 6-8 hours at 5 amps or less....
    The dealership or parts stores do not charge them when they get them.
    Because you want to start with a fully charged 12v battery.

    I didn't suspect the 12V battery, which is 5-6 years old, because the low battery icon didn't light up.[/QUOTE]
     
    #9 ASRDogman, May 23, 2024
  10. Matt N

    Matt N New Member

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    Good Day! Thank you all so much for your responses. The problem hasn't cropped up since replacing the 12V battery a week ago! The old battery still read 12.72V when the terminals were unhooked which was puzzling but I am glad the problem is gone for now.
     
    #10 Matt N, May 30, 2024
  11. ASRDogman

    ASRDogman Senior Member

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    That's good to hear!
    There is NO drain on the disconnected battery, that's why it's reading high.
    Put a brake like bulb across the terminals, or a head lamp bulb and it will go down....

     
    #11 ASRDogman, May 30, 2024
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