12 V Battery Failure Causes More Trouble than You'd expect

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by juliehoskin, Oct 24, 2006.

  1. juliehoskin

    juliehoskin New Member

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    I took my Prius '04 to the dealer a few days ago because as I was driving, there suddenly appeared horrible scraping sounds which seemed to be emanating from the transmission.

    The dealer called back that day with the information that the computer was spitting out all sorts of failure codes and they needed Toyota asistance to interpret.

    A few days later, I was informed that one cell in the 12 V battery had died, causing the erroneous codes and resulting in a glitch from the computer to the transmission.

    The battery replacement (and clearing of the codes) was quoted at $388.

    This seems to be a ridiculous situation for a 12 V battery failure! Has anyone experienced this?

    Information on 12 V battery information online seems to be conflicting, but it also seems like a steep price for a battery replacement (I'm used to batteries costing more in the sub-$100 range!) Is there an alternative to the dealer replacement? (Their literature says it must be replaced by the dealer.)

    Thanks!
     
    #1 juliehoskin, Oct 24, 2006
  2. Cheap!

    Cheap! New Member

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    Are you still under warrenty? If not replace it yourself. Just do the research first. Can't codes be cleard from the service screens on the MFD?
     
    #2 Cheap!, Oct 24, 2006
  3. efusco

    efusco Moderator Emeritus
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    I don't buy that. Either the 12v is working ok or it's not and you should have other symptoms before 'noise from the transmission'.

    Get a list of the codes they got and let us know what they are. Something about this story sequence doesn't make sense to me.
     
    #3 efusco, Oct 24, 2006
  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Why would a 12V battery cause transmission problems?? I'm not technically-inclined in this field but even that doesn't make sense. Also, wouldn't the 12V battery be charging while the car's in motion?
     
    #4 Tideland Prius, Oct 24, 2006
  5. silentak1

    silentak1 Since 2005

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    Random question. I know that the alternator recharges the 12v battery in most cars. Is this the same for the Prius? Or is the 12v a stand-alone battery only used for a few seconds on START?
     
    #5 silentak1, Oct 24, 2006
  6. Marlin

    Marlin New Member

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    <div class='quotetop'>QUOTE(silentak1 @ Oct 24 2006, 11:56 PM) [snapback]337808[/snapback]</div>
    The 12V battery is charged by the Hybrid battery while the car is running.
     
    #6 Marlin, Oct 25, 2006
  7. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(efusco @ Oct 24 2006, 10:56 PM) [snapback]337769[/snapback]</div>
    It depends somewhat on how the cell went bad. If it opened, then the 12v battery would be completely dead; if it shorted, then the 12v battery would become a 10.5v battery. The latter case could cause electronics to run erratically, especially if the voltages were bouncing around a bit.


    <div class='quotetop'>QUOTE(Tideland Prius @ Oct 24 2006, 11:39 PM) [snapback]337793[/snapback]</div>
    The Prius power splitting device (PSD) is just two electric motors and the ICE connected through a planetary gear train. All of the "transmission" functions are done by the computer controlling the two electric motors. If the computer gets weird, it could jerk around those motors.


    <div class='quotetop'>QUOTE(silentak1 @ Oct 24 2006, 11:56 PM) [snapback]337808[/snapback]</div>
    The 12v system charges through a voltage converter from the high voltage system.


    <div class='quotetop'>QUOTE(Cali Julie @ Oct 24 2006, 10:15 PM) [snapback]337747[/snapback]</div>
    This sounds suspicious to me. The battery is small and inexpensive. I suspect the dealer is making up for time spent chasing the problem.
     
    #7 qbee42, Oct 25, 2006
  8. tochatihu

    tochatihu Senior Member

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    I understand that Toyota shops sell the OEM 12 volt battery for about $200. Possible alternatives have been presented here (and in the yahoo groups) before, for the classic model. Not sure that anyone has blazed that trail for the new model yet.
     
    #8 tochatihu, Oct 25, 2006
  9. benlenz

    benlenz Junior Member

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    <div class='quotetop'>QUOTE(tochatihu @ Oct 25 2006, 06:29 AM) [snapback]337910[/snapback]</div>

    I've looked at my Prius 12v battery and it looks exactly like a 12v motorcycle battery. You might check down that route, though I don't really know how you'd be able to tell if it was correct for the application, etc.
     
    #9 benlenz, Oct 26, 2006
  10. juliehoskin

    juliehoskin New Member

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    Just an update on this issue....

    Turns out the battery replacement itself was $193. Still an exorbitant price for a battery change in my view, however, not inconsistent with other dealerships in my area.

    The other $190 was for the labor associated with clearing the codes. I got a printout of the codes (19 of them) most of which involved some variation on the computer not being able to communicate with various other components in the car. (It was indeed a low cell, not simply out of juice, causing low voltage and therefore computer malfunction).

    I'm in the middle of trying to get them to refund some of this money....including an additional $70 from car rental since it took them 5 days! (They just agreed to refunding the car.)

    I've also notified Toyota customer relations....to me this is a design flaw and safety issue that a simple 12 V battery malfunction can cause your transmission to grind so much that you pull off the highway and be so difficult to fix. Also bad news for Prius if the word gets out that a battery change cost $470!

    So if anyone else has this issue or hears of anyone who does, I encourage you to report it so maybe it will get fixed!
     
    #10 juliehoskin, Nov 3, 2006
  11. Tideland Prius

    Tideland Prius Moderator of the North
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    $190 for labour costs clearing the codes? Isn't that part of warranty? unless your car is out of warranty.
     
    #11 Tideland Prius, Nov 3, 2006
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