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Interesting 12V battery story

Discussion in 'Gen 2 Prius Main Forum' started by seilerts, Jun 15, 2011.

  1. seilerts

    seilerts Battery Curmudgeon

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    I had a friend stop by today with his flaked-out 2007. He had it jumped before he brought it over due to a dead 12V battery. With the car off, it read 6V! As soon as I connected the jump-pack, the car started immediately i.e. no one pressed the power button, the key (non sks) was not inserted, the MFD showed the Abnormal Transmission Lock Mechanism message, and most of the yellow brake/abs/vsc warning lights were on. Cycling off/on with the jump pack still attached made it Ready with no lights. I disconnected the jump pack and drove the car inside to be out of the sun.

    After disconnecting and replacing the old battery with a new one, the car fired right up into the same weird state with the error message and warning lights as soon as I connected the negative terminal. That's the part that to me is the strangest. Anybody know why shutting the car off with a dead battery would cause it to wake up in a semi-operational state? I would have thought that a complete battery disconnect whether dead or alive would cure all ills.

    Anyway, one more off/on cycle and the car was fine.
     
    #1 seilerts, Jun 15, 2011
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  2. patsparks

    patsparks An Aussie perspective

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    Restart the car 5 times, I think that will fix it.
    I have no idea why this happens, it has happened to me to.
    You might need to hold the power button in for a while to switch off.
     
    #2 patsparks, Jun 15, 2011
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  3. Hal W

    Hal W New Member

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    Weird stuff happening with that Prius!!! Things like that can be very dangerous! You would think it could be programmed so you would have to enter a code IE like the radio, before starting the car after battery disconnect? Hal
     
    #3 Hal W, Jun 15, 2011
  4. qbee42

    qbee42 My other car is a boat

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    The ECUs, like all digital electronic devices, require carefully choreographed starting sequences. Low voltage creates uncertain race conditions, where the ECUs can power up improperly. Some of the state information persists through several power-up sequences, which is why you may need to power up a few times to get everything back to normal.

    Tom
     
    #4 qbee42, Jun 15, 2011
  5. David Beale

    David Beale Senior Member

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    Brake capacitors affecting the system?
    Be aware, on and off have a different meaning in a Prius and most modern electronics. It's merely a state of operation, not a state of the power supply.
     
    #5 David Beale, Jun 15, 2011
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Thanks for sharing that story. This is a good example why it is better to replace the 12V battery at the first sign that it is weak, rather than hobble along with the use of a jumpstart device.

    An excellent point. The skid control and SRS ECUs can maintain some information (at minimum, stored DTC) even when 12V voltage is disconnected.

    That may be a contributing factor with regards to maintaining the state of the skid control ECU.
     
    #6 Patrick Wong, Jun 15, 2011
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  7. koolingit

    koolingit Member

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    Hobbit documented this happening to him when he disconnected his 12 volt battery while the car was on 'Ready' and then shutting down. When he reconnected the 12 volt battery, he got the same strange wake up.

    Shutting down and then restarting corrected everything. See: http://techno-fandom.org/~hobbit/cars/prius-12V/
    It's all interesting, but what you're looking for is way down near the bottom.
     
    #7 koolingit, Jun 15, 2011
  8. The Critic

    The Critic Resident Critic

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    I had that happen to me as well (sort of) after I replaced the 12v battery on my friend's 06. When you powered the car on, all of the warning lights came on but the car was not in ready mode. Yet, you did not hear any beeping. One reboot sequence corrected the problem.
     
    #8 The Critic, Jun 17, 2011
  9. andyprius

    andyprius Senior Member

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    It's like rebooting a computer, except the feedback is better and there are three (?} ECUs:nono:
     
    #9 andyprius, Jun 18, 2011
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