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Auxiliary Battery - Diagnosis??

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by StevL, May 24, 2010.

  1. StevL

    StevL Junior Member

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    My wife's Prius has run perfectly for years, only has 27k miles on it, is garage kept, and we live in the South with no snow or prolong cold weather.

    This past Saturday it started running on gas only, the MFD showed the main battery down to two purple bars then down to one. It never ran on electricity nor did it ever charge the main battery. Ran on gas all day.

    The next day (Sunday) I took it for a drive to see if something had changed. It did, now it does what it is supposed to do except one thing the MFD revealed; the main battery charges to full green status within minutes of driving (never did this before), while stopped at a traffic light it will discharge all the way down to the two purple bars (never did this before either). Minutes later it's back to full green.

    There are no warning lights on. The dealer I took it to this morning is having to call Toyota but their first indication is they think it is the "Auxiliary Battery".

    This just doesn't make sense to me, on the surface it looks to be the main battery to me.... I'm thinking if it runs on gas fine then why the auxiliary battery?

    Help!! Thoughts!!

    Cheers,
    Steve
     
    #1 StevL, May 24, 2010
  2. jdenenberg

    jdenenberg EE Professor

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    Get to a dealer. Its probably still under warranty.

    JeffD
     
    #2 jdenenberg, May 24, 2010
  3. StevL

    StevL Junior Member

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    I did, this is why I'm asking, doesn't make sense to me.

    Steve
     
    #3 StevL, May 24, 2010
  4. jayman

    jayman Senior Member

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    The Prius 12 vdc battery doesn't appear to last very long, and can cause many strange symptoms when it is starting to fail

    I had odd symptoms less than a year after I got my '04 Prius, but leaving it hooked up all the time to a VDC Battery Minder cured it
     
    #4 jayman, May 24, 2010
  5. jdenenberg

    jdenenberg EE Professor

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    When the 12v battery is weak, but not dead, the computer initialization fails and it gets confused. Check the 12v battery voltage either directly with a meter or using the MFD in maintenance mode. Directions are available in many discussion threads or at: 12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007, 2008, 2009 and 2010 with installation kit. The battery voltage should be above 12v in accessory and stay above 12v when you add a load (eg lights). In ready mode the voltage should be about 14 volts.

    JeffD
     
    #5 jdenenberg, May 24, 2010
  6. StevL

    StevL Junior Member

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    I do not understand why the main batter charged and discharged so rapidly, but the auxiliary battery was replaced and it cleared up the problem.

    Still confused but happy.

    Cheers,
    Steve
     
    #6 StevL, May 25, 2010
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Probably because the weak auxiliary battery caused the battery control ECU to be confused. The SOC indications on the MFD may have been bogus.

    Your situation provides yet another example why I prefer to replace the 12V battery periodically as a preventive move, rather than waiting for it to fail.
     
    #7 Patrick Wong, May 25, 2010
  8. docchaez

    docchaez Junior Member

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    Hey guys,

    Sorry to bring up an old post. I have 04 Prius with 136k trouble-free miles until I encountered check engine lights along with the red triangle yesterday. The OBD-II code reads P 0A80. Is it possible that an old 12 V battery is triggering the code, rather than the hybrid battery? Mine is still the original came with the car when it was new.
     
    #8 docchaez, Apr 15, 2013
  9. edthefox5

    edthefox5 Senior Member

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    That is Hybrid battery death. Its detecting one or more cells are out of range. Usually accompanied by sudden charge-empty-charge indication on the MFD.

    Lots of discussions on alternative battery sources and or repairing the pack yourself if electrically knowledgeable.
    Search around on this site.
     
    #9 edthefox5, Apr 15, 2013
  10. docchaez

    docchaez Junior Member

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    Thanks Edthefox5. I was hoping a bad 12V battery would make the system confuse and threw out that code, which would be a much less costly repair that replacing the hybrid battery. :-(
     
    #10 docchaez, Apr 15, 2013
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It would not hurt for you to replace the 12V battery now since you indicated it is original equipment. However it is likely that your car needs a new traction battery as well.
     
    #11 Patrick Wong, Apr 15, 2013
  12. docchaez

    docchaez Junior Member

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    Thanks Patrick. I just can't get over the sticker shock for replacing the hybrid battery.
     
    #12 docchaez, Apr 15, 2013
  13. docchaez

    docchaez Junior Member

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    BTW anyone has any recommendation in Northern VA area for such repair/replacement? Local dealers quoted me anywhere from $4400 to $3500.
     
    #13 docchaez, Apr 15, 2013
    uuiz likes this.
  14. cwerdna

    cwerdna Senior Member

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    #14 cwerdna, Apr 15, 2013
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