12v battery runs down while driving

Discussion in 'Gen 2 Prius Main Forum' started by Mikaho, Aug 6, 2019.

  1. Mikaho

    Mikaho New Member

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    2007 Prius 5. 187k miles. One year old new hybrid battery. Just had inverter water pump replaced. Right after that the car started to have random dash lights. Brake light wood come on then turn off. Checked brakes and fluid, looked good. Then a steady alarm beep would come on (like when you get out when the key fob is inserted.) Again it would be intermittent. Come on, then turn off and not come on for a day or more. Then the AC would stop blowing cold air. Again, briefly, then it would stay again.

    Finally, while driving home the brake light and the alarm came on and the anti lock brake light came on. Shortly after, the ac stopped the blowing cold. Then the red triangle came on and the car lost power. I pulled over off the road and then the dash went dark and the car died and would not start at all. And the windows wouldn't roll up, radio wouldn't play. When AAA got to me, the driver mentioned seemed like the 12v battery was dead. But towed to the house and sure enough the 12v was dead. But it charged over night and was showing 13v in the morning.

    Since then, the car appears to run fine in the mornings before the heat of the day. But when driving home, of I drive more than about 30 minutes I start to get the same symptoms but it hasn't died since. But I notice the fully charged battery is putting out 13v and it seems to drop about 0.5 volts each day of driving and when it starts to have the intermittent symptoms, it is going to show a bit under 12v. So I can drive the car 2 or three days then have to put a charger on the battery to top it off.

    What could be causing this?

    Thanks for any ideas.
    Michael
     
  2. bisco

    bisco cookie crumbler

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    welcome!

    a bad battery?
     
  3. jerrymildred

    jerrymildred Senior Member

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    Sounds to me like the battery is OK if it takes and holds a charge.

    I'd put a meter on the 12V while the car is running. It should read about 14 volts. If it's not, then it would be something in the DC/DC converter in the inverter.
     
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  4. Calimobber

    Calimobber Junior Member

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    The DC to DC charger has 2 modes. Its like 13.8 and 14.5. off the scan gauge mines normally 13.8v.

    I agree start the car and see what the 12v charger is doing.
     
  5. bisco

    bisco cookie crumbler

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    a dead 12v that is holding 13v has a problem, or a mistake is being made in the testing procedure.

    put a load on it and watch the fun
     
  6. Skibob

    Skibob Senior Member

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    How old is the 12v? Check the negative to body connection. Sometimes that Bolt gets lose and does strange things.
     
  7. ChapmanF

    ChapmanF Senior Member

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    +1
     
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  8. SFO

    SFO Senior Member

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    Welcome to PriusChat!!
    Given the above description/symptoms (12v not charging, AC not working, drives fine for 30 mins, etc). Let us take a WAG and assume that the inverter in actually overheating (DTC P0A93).

    Which may be caused by :
    • The hoses for the newly installed inverter coolant pump being switched around during the R+R process
    • The inverter coolant not being properly refilled and/or bled
    • The new inverter coolant pump malfunctioning
    If there is a red triangle (aka triangle of death) and other "random dash lights" displayed, one should at a minimum open up the owners manual to decode the displayed icons for their own knowledge base. Afterwards, locate an appropriate hybrid compatible OBD2 code reader, and read the stored codes (DTCs).

    Please post all of the retrieved codes here, then we provide you with a more meaningful coarse of action.
     
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