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No power at all, sometimes...

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Erisraven, May 21, 2021.

  1. Erisraven

    Erisraven Junior Member

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    Location:
    Louisville KY
    Vehicle:
    2008 Prius
    Model:
    ----USA----
    My 2008 has an issue, but I can't tell where in the system it is.
    Sometimes when I get in, everything will be dead, as if there is no battery power at all. Open the hood, jump it for a couple of seconds. Starts up just fine.
    I did the built in diagnostic right after start, and the battery is reading 13.7.
    If the battery was dead, I don't think I'd get that would I? I suspect there's a short somewhere in the system.
    I will run any test you suggest that I'm capable of. I have to get this car stably working. Suggestions?
     
    #1 Erisraven, May 21, 2021
  2. dolj

    dolj Senior Member

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    The car is READY by this stage, right? All that tells you is the DC/DC is working, but nothing about the battery.

    Check the voltage of the battery at the front jump point after the car has been off for two hours, then see what the voltage drops to when you put the headlight on high-beam. What does the voltage stabilize to?

    I doubt there is a short, but check for loose connections – the two battery terminals and where the negative strap connects to the car body.
     
    #2 dolj, May 22, 2021
    jerrymildred likes this.
  3. sam spade 2

    sam spade 2 Senior Member

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    That is the charging voltage, NOT the battery voltage.
    Rather than a short, you probably have an intermittent OPEN circuit.
    How old is the battery ?

    Most common causes are: A defect inside the battery......a worn out battery......or a loose main battery cable at EITHER end of the main cables.
     
    #3 sam spade 2, May 22, 2021
  4. bisco

    bisco cookie crumbler

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    replace the 12 volt, problem solved
     
    #4 bisco, May 22, 2021
  5. rjparker

    rjparker Tu Humilde Sirviente

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    Could be a bad battery that holds a charge when off for a short time but can't maintain adequate voltage overnight.

    Realize the car draws current all the time even when off. This is called a parasitic draw. 15ma-30ma is normal and will allow a new battery to start the car even after three weeks. As the battery gets old that time slowly decreases.

    A free battery test at most auto supplies checks the battery. A mechanic could do a parasitic draw test to verify no unusual off state loads exist.

    Most find the 12v battery is worn out, replace and forget it for five to seven years.
     
    #5 rjparker, May 22, 2021
  6. SFO

    SFO Senior Member

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    Welcome to PriusChat!!
    How many hours per week were you driving this vehicle?

    Before you start or jump start it, measure the resting voltage at the jump points under the hood, this requires a voltmeter or a multi-meter.

    FYI : your posts are being moderated until you've post 5 times.
     
    #6 SFO, May 22, 2021
  7. Erisraven

    Erisraven Junior Member

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    2008 Prius
    Model:
    ----USA----
    Moderation: good to know. That's what I get for being a lurker and not jumping in earlier. I grabbed a multimeter and will test. Also bought a replacement battery and will be getting someone to install it for me this week. Thank you all for the pointers and the help.
     
    #7 Erisraven, Jun 2, 2021
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