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12v issue

Discussion in 'Gen 2 Prius Main Forum' started by Stepperez, Apr 21, 2017.

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  1. Stepperez

    Stepperez Junior Member

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    My 12v is failing three times a day!!! I have to have my car so luckily I know how to change it and have three of them.. I know if I keep it up I am gonna cause permanent damage. The vcs and yellow brake light are on all the time. I know its not the hybrid batt. I am thinking its something with the electric motor or regenerative braking system. I need so new eyes please
     
    #1 Stepperez, Apr 21, 2017
  2. WilDavis

    WilDavis Senior Member

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    What codes? (If any...) There are always codes! Hi thee to someone with a scanner (...so any codes might be read!) Good luck!
     
    #2 WilDavis, Apr 21, 2017
  3. kenoarto

    kenoarto Senior Member

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    How old is the battery? Not that it matters much. Once it's been drained two or three times, the battery is a goner.
     
    #3 kenoarto, Apr 21, 2017
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Check the inverter coolant reservoir for fluid turbulence when the Prius is READY. If you do not see this, the inverter coolant pump has failed and that is the root cause of your problem. The DC/DC converter in the inverter will overheat and shut down, putting strain on the 12V battery which will quickly discharge.

    2. If that reservoir looks OK regarding turbulence, measure voltage across the 12V battery using a digital multimeter, when the Prius is IG-OFF and also, when it is READY; and report your measurements.
     
    #4 Patrick Wong, Apr 21, 2017
    valde3 likes this.
  5. Stepperez

    Stepperez Junior Member

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    2007 Prius
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    V
    Y'all have to cut me some slack if I ask stupid questions, I'm just learning. So the 12v will not hold but a couple of charges? There are no codes I have checked and re checked. I do a Lot of traveling for work and so I did figure out traveling on the interstate in the B gear helps but should that be necessary? ( I decided to buy the car from the customer ) it almost has to be the 12v. Everything else reads fine. I'm getting a brand new one tomorrow. Any suggestions? Oh and advice on the brakes...once or twice I have had to come to a screeching halt because the battery just dies. I'm sure I need to check the tires for bed spots but what about the brakes? They are kinda touchy now.
     
    #5 Stepperez, Apr 25, 2017
  6. kenoarto

    kenoarto Senior Member

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    Suggest you do a google search on "car battery deep discharge damage"
     
    #6 kenoarto, Apr 25, 2017
  7. andrewclaus

    andrewclaus Active Member

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    Do not drive in B mode. Read the owner's manual. It's for "engine braking" only.

    From your post, it sounds like you think the "B" mode is charging the 12V. That's not the case. You're making the hybrid system work harder.

    If you don't know how to check brakes, get the car to a brake shop for an estimate of what needs to be done. Don't mess around with the brakes without someone qualified supervising and checking your work.

    Have you investigated the inverter cooling pump operation (see post #4) yet?

    If you're going to work on this car, you'll need a Prius-specific scanner. Generic OBD-II scanners won't read hundreds of codes specific to the Prius.
     
    #7 andrewclaus, Apr 25, 2017
  8. fuzzy1

    fuzzy1 Senior Member

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    If the 12V battery is dying while you are moving, then it is not getting charged. Go back to Post #4 and do the checks Patrick suggests. The inverter section that feeds the 12V system could be dead, or could be simply overheating (from cooling pump failure) and shutting off.
    When they are touchy, do they feel like manual brakes (lots of foot pressure required), or like regular power brakes? If the former, I'll continue with looking at 12V system failure. If the later, does it include any high pitched squeal? Then your front brake pads might be worn out. Though when a rear drum shoe on one of my past cars, it grabbed without any squeal.
     
    #8 fuzzy1, Apr 26, 2017
  9. bisco

    bisco cookie crumbler

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    how many miles on her?
     
    #9 bisco, May 10, 2017
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