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Master caution light / dead 12 volt battery

Discussion in 'Gen 2 Prius Technical Discussion' started by GreenGene, Nov 21, 2012.

  1. GreenGene

    GreenGene New Member

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    Mar 31, 2006
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    Location:
    Northern Virginia
    Vehicle:
    2006 Prius
    So our '06 Prius has been very, very reliable, and we have a bit over 105K miles on it now. But we have a problem that the dealer hasn't been able to confirm, much less fix.

    Probably three months ago now I began to notice that, from time to time, when I started the Prius, the master caution light (red triangle) would come on for 2-3 seconds. At no point did it stay on, and at no point did the Prius fail to start. So, it was an intermittent caution light of brief duration.

    Then we had a bad storm coming (Sandy) and although it wasn't nearly as bad here (N. VA) as it could have been, I put the Prius in the garage, and it sat there for three days. When I went out to start it, the 12 volt battery was dead.

    Fortunately I always back into the garage, and so jump starting the Prius - although it was my first time doing so - was no problem, and I got it to the dealer that morning. They tested the battery, and it was fine. They checked the codes, and all was well. It was as if the battery had never died. AND we stopped seeing the master caution light ... until two days ago, when my wife said that she saw the light a couple of times when she was out running errands.

    Has anyone ever had this problem, or anything similar? Is it possible to have a problem with the 12 volt battery and/or electrical system that doesn't show up in the codes? And am I wrong to lose confidence in this very, very reliable car??

    Many thanks.
    GreenGene
     
    #1 GreenGene, Nov 21, 2012
  2. jdcollins5

    jdcollins5 Senior Member

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    Location:
    Wilmington, NC
    Vehicle:
    2010 Prius
    Model:
    III
    If this is your original 12V battery, replace it. When this battery begins to fail you can get all sorts of weird things happen.

    The car is still very reliable, it just needs a new battery.
     
    #2 jdcollins5, Nov 21, 2012
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Vehicle:
    2015 Prius
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    Two
    1. When the 12V battery dies, most DTC will be erased. Only DTC logged by the skid control and SRS ECUs will be retained. Therefore it is pointless to check for DTC after the 12V battery died, unless you were having a problem with the braking system or airbag system.

    2. If the 12V battery cannot withstand the car being parked for three days without dying, it obviously has low capacity and I would replace it now. It is a waste of time for the dealer to test the battery and I hope you did not pay for that test.

    3. Check the engine oil level when the Prius is parked on a level surface and has been IG-OFF at least 5 minutes. There is no warning for a low oil level other than the master warning light coming on.

    4. Have the fob batteries been replaced yet? If not, replace them now.
     
    #3 Patrick Wong, Nov 21, 2012
    Andyprius # 1 likes this.
  4. GreenGene

    GreenGene New Member

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    Mar 31, 2006
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    Location:
    Northern Virginia
    Vehicle:
    2006 Prius
    Many thanks. Sounds like, despite what the dealer told me, it's time for a new battery. I didn't realize the codes would be erased when the battery dies, although that certainly makes sense. The engine oil is fine; the fob batteries were replaced last year; no, I didn't pay anything for the battery test or for them to check the codes.

    I think I'll call the dealer now, and see if I can get a battery put in today.
     
    #4 GreenGene, Nov 21, 2012
  5. yankkesrule

    yankkesrule Junior Member

    Joined:
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    Location:
    Masshole
    Vehicle:
    2001 Prius
    Model:
    N/A
    The car will very commonly throw a code for the park mechanism. When the battery is weak/dead it has an issue fully going into/out of park. A new battery should take care of your issues.
     
    #5 yankkesrule, Feb 24, 2013
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