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Electronic Fault in the START system?

Discussion in 'Gen 2 Prius Technical Discussion' started by DeadPhish, Jun 6, 2009.

  1. DeadPhish

    DeadPhish Senior Member

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    I've noticed four times over the last week that when I shut down my Prius that it immediately comes back to life in Accessory Mode??? Weird, this never occurred before.

    The Fob is always in my pocket. I hit Park then Power OFF but it will sometimes go OFF then right back to ACC mode. If I power on with my foot on the brake then power OFF again it stays OFF.



    I'm thinking ...
    1. 12v battery is getting low and screwing with the electronics
    2. a faulty sensor
    3. a low battery in the Fob
    4. a traction battery beginning to act up..doubtful
    See details of my 05 in my sig. Does anyone have any experience with a situation like this?
     
    #1 DeadPhish, Jun 6, 2009
  2. richard schumacher

    richard schumacher shortbus driver

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    Data trumps (or at least informs) speculation :_>

    If the little red LED on the fob no longer flashes when you press a button the fob battery should be replaced.

    Test the 12V battery, either
    - with a voltmeter at the jump point under the hood; with the car OFF it should be between 12.5V and 12.8V. If it's less than 12.0V it should be replaced.
    - using the self-test procedure shown here:
    http://www.myhybridcar.com/forums/toyota-prius/217-checking-12v-battery-health.html
     
    #2 richard schumacher, Jun 6, 2009
  3. DeadPhish

    DeadPhish Senior Member

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    The fob on my 2005 doesn't have an LED indicator of any kind.

    I ran the above procedure and found the following
    step 1 at ACC only the battery was at 11.1-11.2 v
    step 2 with a load on it... i didn't write the values down
    step 3 with full power on the battery reading was 14.1-14.2v

    additional data:
    randomly the clock will reset to the default of 1:00

    From your criteria it does seem if the 12v is giving up the ghost, no?
     
    #3 DeadPhish, Jun 6, 2009
  4. qbee42

    qbee42 My other car is a boat

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    A good battery should be at around 12.8 V when not being charged. Yours is too low.

    Tom
     
    #4 qbee42, Jun 6, 2009
  5. timberwolf

    timberwolf New Member

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    For your step 1), mine readings vary between 11.9 to 12.1 which has done from new. The test using the MFD still puts a load on the battery, and those figures that Richard quotes sound like the voltages that you'd only get with the car completely off and using a Digital Multi Meter measuring at the battery terminals.
     
    #5 timberwolf, Jun 6, 2009
  6. richard schumacher

    richard schumacher shortbus driver

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    The ACC load should be less than one Amp, which a good battery would barely notice, so I strongly suspect a failing 12V battery. If you can borrow a voltmeter, the jump point voltage with the car OFF would settle it.
     
    #6 richard schumacher, Jun 7, 2009
  7. hschuck

    hschuck Member

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    The indicator is difficult to see when not activated. Hold the fob so that the lock button is at the top. The indicator is to the right of the lock button on the raised bezel. It should illuminate when one of the buttons is pressed; if a smart key fob it will also illuminate when communicating with the car.
     
    #7 hschuck, Jun 7, 2009
  8. Celtic Blue

    Celtic Blue New Member

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    That be D-E-A-D, dead, deceased, no longer amongst the living, an ex battery. :rip: Whenever I have a vehicle battery in that range it begins behaving more as anchor than as power storage device. They don't rehabilitate well either.
     
    #8 Celtic Blue, Jun 7, 2009
  9. timberwolf

    timberwolf New Member

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    How much of a volt drop would you expect to see with the MFD method compared with a digital voltmeter measure the battery not under load? 0.5 volts?
     
    #9 timberwolf, Jun 11, 2009
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