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How to get to 12v battery diagnostic check

Discussion in 'Gen 3 Prius Main Forum' started by Robby2010IV, Jul 13, 2018.

  1. Robby2010IV

    Robby2010IV Junior Member

    Joined:
    Oct 25, 2016
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    Location:
    Irvine
    Vehicle:
    2010 Prius
    Model:
    IV
    I have a 2010 model IV with 150,000+ miles.

    A few weeks ago, I noticed my car horn would beep slightly whenever I start my car.

    Someone suggested checking my key remote batteries. Unless both batteries are low it beeps with both keys.

    The next suggestion is to check the 12v battery. I found a Youtube video for a Gen 2, i tried the same but could not get a digital display value for 12v usage.

    If you know how, please provide detailed steps that takes me to the 12v battery display.

    Thanks!
     
    #1 Robby2010IV, Jul 13, 2018
  2. bisco

    bisco cookie crumbler

    Joined:
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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
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    Plug-in Base
    just take it to any auto parts store for a free load test.
     
    #2 bisco, Jul 14, 2018
  3. Lucifer

    Lucifer Senior Member

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    Vehicle:
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    Plug-in Advanced
    No need to test, just get a new 12v, make sure you trickle charge it overnight before installing.
     
    #3 Lucifer, Jul 14, 2018
  4. ChapmanF

    ChapmanF Senior Member

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    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Once you're in the MFD diagnostic screens (I assume you have one of the touch-screen models; I have no idea what diags are available in the LCD radio-only versions), look for the "vehicle signal check" screen. The voltage is there, along with the status of the parking brake, taillight, and reverse signals.

    Be aware that the voltage shown there is typically a good fraction of a volt (say, .6 or .7) lower than what you would measure at the battery itself, which means if you post the reading on PriusChat you may attract responses that emphasize how low it would look on a voltage-vs.-state-of-charge chart, and will have to keep your head about you.

    -Chap
     
    #4 ChapmanF, Jul 14, 2018
    hec24 likes this.
  5. yeldogt

    yeldogt Active Member

    Joined:
    Jan 20, 2012
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    Location:
    NE
    Vehicle:
    2011 Prius
    Model:
    Five
    We have them on a 4 year replacement -- if you still have the original .... replace it. It seems the OE batteries are not as strong as the better replacements. Its an odd size and very small.
     
    #5 yeldogt, Jul 16, 2018
  6. bobzchemist

    bobzchemist Active Member

    Joined:
    Aug 2, 2016
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    Location:
    Kennesaw, Georgia, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    This is for the NAV display:

    1. Start with headlights off and car off. Have everything on car off (radio, etc.) It may be best to do this after the car sits overnight.
    2. Keep foot off brake pedal
    3. Push POWER Button twice
    4. Hold in "INFO-PHONE" button on right side of NAV/Headunit display and keep it in while doing next step.
    5. Turn headlights on and off three times quickly - hidden diagnostic menu comes up. Release "INFO-PHONE" button.
    6. Press "Function Check/Settings" on NAV display. New menu comes up.
    6. Press "Vehicle Signal" on NAV display.
    7. Battery Voltage is displayed without load. Record it.
    8. Turn headlights on, radio, press brake pedal, anything else you can think of to put a load on the battery. Battery Voltage is displayed with load. Record it. Turn off everything.
    9. Place foot on brake pedal and Press POWER button to turn on the car. (Ready status). Record new reading.
    10. Press POWER button to turn off car, which takes you out of diagnostic mode. Car and display will now behave normally.

    Search here for info on what voltage readings indicate a healthy battery. Or, don't bother and just replace the battery.
     
    #6 bobzchemist, Jul 26, 2018
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