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Dead 12V battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PriBeeee, Jan 16, 2014.

  1. PriBeeee

    PriBeeee Junior Member

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    I've spent hours looking for a post from somebody whose Gen II had the same problem as mine, but couldn't find exactly the same. The car was fine last Thurs night when it was last driven, but dead as can be when I tried to start it yesterday. No signs of life at all. The doors unlocked after I hooked up a portable jump starter, and the dashboard lit up with the usual icons, but the car wouldn't start. Using the "engine start" setting on a battery charger produced the same result. The icons light up and there's a low level hum, but the car doesn't start. The 12v battery was replaced 10k miles ago in Feb 2011. Before I bother pulling the back of the car apart to get to the 12v battery, I'd like opinions on whether that's a useless undertaking, or if there's a chance it's the battery again. Thanks for ideas and suggestions.
     
    #1 PriBeeee, Jan 16, 2014
  2. JC91006

    JC91006 Senior Member

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    I would check the voltage on your battery first. If it's in an acceptable range, 12.1 volts or above, then I would disconnect the negative battery terminal for 30 seconds and allow the car to reset. Reconnect and try to start the car again.

    There may be an issue that's preventing the car from starting. A scan gauge will help determine if there are any DTC's logged.
     
    #2 JC91006, Jan 16, 2014
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Your car has the same issue as many Prius during wintertime: a dead 12V battery. If the car was fine one day and dead the next, a dead 12V battery is the most likely cause.

    1. The 12V battery is almost three years old yet the car has logged only 10K miles during that period. Unless you have regularly charged the 12V battery (once per month), it is likely that the battery has died due to lack of adequate charging.
    2. In fact, it sounds like the 12V battery may have a shorted cell and is so dead that it is sucking power from the portable jumpstart device and is preventing the Prius from starting.
    3. Do not use the "engine start" feature on the battery charger. That pumps excessive voltage into the 12V battery and may damage the Prius electronics.
    4. If you disconnect the 12V battery, and use the jumpstart device at the battery cables, you probably can get the Prius to become READY. Then, take the opportunity to visit your local Toyota dealer's parts dept and buy a new 12V battery.
    5. Finally, use your 12V battery charger monthly and keep the new 12V battery charged up, to lengthen the service life that you will realize from the battery.
     
    #3 Patrick Wong, Jan 16, 2014
  4. bisco

    bisco cookie crumbler

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    are you stepping on the brake with adequate pressure to overcome the interlock switch? do the brake lites come on?
     
    #4 bisco, Jan 16, 2014
  5. PriBeeee

    PriBeeee Junior Member

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    End result: It was a dead cell in the battery. The new non-OEM battery with an 84-month warranty cost the same as the OEM battery with a one-year warranty I put in three years ago. Thanks for the suggestions.
     
    #5 PriBeeee, Jan 25, 2014
  6. nh7o

    nh7o Off grid since 1980

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    The shorted cell is due to sulfation as a result of lack of charging. There are desulfating pulse type battery tenders available, which would be recommended as the way to keep that battery alive longer. It should be placed right at the battery terminals, as close as possible. I have one left permanently connected, and run the AC cord out the hatch and left plugged in when the car is not in use.
     
    #6 nh7o, Jan 25, 2014
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