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Battery Discharging when lights are on

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jeffrey Griswold, Oct 20, 2014.

  1. Jeffrey Griswold

    Jeffrey Griswold New Member

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    Hello I was wondering if anybody here could help me, I am having an issue with my 2006 Toyota Prius. The battery seems to be fine, but when I turn on the headlights the battery suddenly starts dropping sharply and the lights quickly dim. I turn them back off and it starts charging properly again. It only does it when I turn on the headlights. Weird part is if I hit a bump just right sometimes it goes back to normal for a while, but then starts discharging again. Any help on this would be much appreciated.
     
    #1 Jeffrey Griswold, Oct 20, 2014
  2. PriusGuy32

    PriusGuy32 Prius Driver Extraordinaire

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    I would start by checking your 12v battery and connections. Make sure the ground is tight on the body and battery post.

    Also, check the health of your 12v battery.
     
    #2 PriusGuy32, Oct 20, 2014
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  3. Easy Rider 2

    Easy Rider 2 Senior Member

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    Which battery is it that "starts dropping sharply" ??

    Either way, it sounds to me like you have a short in the headlights somewhere.
    Could be a bulb, corroded socket or (if HID) a ballast.
    Sure sounds like something is drawing excessive current.
     
    #3 Easy Rider 2, Oct 21, 2014
  4. Britprius

    Britprius Senior Member

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    The first place to check is the negative battery lead where it joins the bodywork below the rear light. This is a known source of trouble either being loose or corroded. Remove clean refit and tighten.

    John (Britprius)
     
    #4 Britprius, Oct 21, 2014
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  5. Jeffrey Griswold

    Jeffrey Griswold New Member

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    I believe it is the HV battery as it is the one shown on the energy monitor that seems to drop.
     
    #5 Jeffrey Griswold, Oct 21, 2014
  6. Easy Rider 2

    Easy Rider 2 Senior Member

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    If that is true, I think you should be REALLY concerned, maybe to the point of not using the headlights at all until you find out what the problem IS and get it fixed.
     
    #6 Easy Rider 2, Oct 22, 2014
  7. GregP507

    GregP507 Senior Member

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    The voltage drop could be caused by a number of things.
    In order of likelihood (in my opinion):
    • Bad battery.
    • Poor connections.
    • Faulty component.
    • Short circuit.
     
    #7 GregP507, Oct 22, 2014
  8. valde3

    valde3 Senior Member

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    Problem sometimes goes away after hitting bump so it’s probably bad connection somewhere. But it can be in inverter, hybrid ecu, battery ecu, hv-battery, 12V battery, wiring, or some other place.

    If you connect techstream to car and problem is present it should be possible to narrow down problem. Or if there is fault codes present (there can be even if fault lights haven’t been on.

    -First check your 12V battery Toyota Prius: How to Check the 12v Auxiliary Battery Health - PriusDIY.com
    -If it ok then check its ground cable as suggested by Britprius.
    -If its ok then check that there isn’t codes (you’ll need hybrid specific scanner (techstream is best and cheap)).
    -If there isn’t any code then you’ll have to diagnose problem with techstream connected to car while problem is present.
     
    #8 valde3, Oct 22, 2014
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