2008 Prius Not Starting Unless Door Locks Cycled

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JimCog, Jul 11, 2022.

  1. JimCog

    JimCog New Member

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    Hello, new user here but I've benefited from this forum for many years to diagnose issues on my '08 prius so thanks to everyone for their trials and errors and knowledge. I recently had my prius towed to the dealer due to it not starting even after a jump. I assumed the 12V batt had died. The battery is a little over three years old now and the lights have been left on in the car overnight a few times so I assumed the battery was done. The dealer said the battery was fine after a check and said there appeared to be nothing wrong as they couldn't replicate the issue. As soon as I got the car back home and tried to restart it, it of course didn't start. All the typical lights on the dash are on with no warning codes but the car won't turn on. When I try to shift it into reverse it instead goes into neutral.

    After some deep web searching, I did find another user who said that unlocking/locking the doors first allowed the car to start up. I've never had to this to this point but tried it and now the car starts but only if I cycle the door locks. My only thought was that the 12V battery connections could be loose but they appear tight after looking at them yesterday.

    There seems to be some type of electronic issue here where the electronics are asleep and the door locking/unlocking is able to "wake" up a controller to get the car ready to drive but this is beyond my knowledge. Any advice on what to check/try would be greatly appreciated.
     
    #1 JimCog, Jul 11, 2022
  2. JC91006

    JC91006 Senior Member

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    If you suspect the 12v battery is done, then I would just replace it. A quality battery from the dealership may be able to withstand a few discharges (the ones you mentioned), but if it's a cheaper battery from a 3rd party, it won't perform so well. Since it's 3 years old, I would just replace it and move on.
     
    #2 JC91006, Jul 11, 2022
  3. bisco

    bisco cookie crumbler

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    what code reader are you using?

    do the brake lights come on when you step on the brake?

    have you tried a jump start?

    do you own a volt meter?
     
    #3 bisco, Jul 11, 2022
  4. Another

    Another Senior Member

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    Depending on the brand and model of the 12v battery, it may still have some prorated warranty credit remaining even after three years. Before you trash it, you may want to check for warranty status.
     
    #4 Another, Jul 12, 2022
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    +1 to everything from bisco's post.

    If the brake light switch works (even when the car won't go READY?), and the 12V battery voltage is "good" (ideally 12.6-12.8V with the car off, and around 11.5- 12.0V with ignition switched ON but not ready. the higher V the better )

    Then I would be using a "high end" scantool to check all ecu's for codes and look at data for things like power control ecu. Techstream on a laptop (+ a VCI cable) is good. Autel AP200 or ThinkDiag app -either with its own OBD2 device are also good choices. Use the search function to learn more.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Jul 12, 2022
  6. JimCog

    JimCog New Member

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    Update! It turns out the issue was the brake light switch even though it didn't really shows signs of being faulty. Car has been fixed for a week now and starts up every time without issues. Word to the wise, don't assume it's the 12V battery unless you've tested it and found that the voltage is less than what it's supposed to be.
     
    #6 JimCog, Aug 2, 2022
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