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MPG Gauge INCOHERENT AFTER 12V CHANGE

Discussion in 'Prius v Technical Discussion' started by Remyfla, Dec 2, 2019.

  1. Remyfla

    Remyfla New Member

    Joined:
    Dec 1, 2019
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    Location:
    alabama
    Vehicle:
    2012 Prius v wagon
    Model:
    III
    I purchased a 2012 Prius V last year with 65K miles. I've had no problem with it until last week when it wouldn't start. All the lights but READY were on and from what I read that indicated the need for a new 12V. The car was OFF to my knowledge when I installed the 12V. As I had the NEGATIVE lead already attached to the car, when the POSITIVE cable made contact with the battery's POSITIVE post there was just a slight arc of electricity. I didn't think anything of it and the vehicle was started and ran without a problem. However when I started to drive I noticed my MPG indicator was sporadically going from 9.9 to 99.9 and everywhere in between! I just drove 1400 miles in the car and it did it the entire trip. Anyone know how to correct this problem? THANK YOU
     
    #1 Remyfla, Dec 2, 2019
    Last edited: Dec 2, 2019
  2. Centerpunch

    Centerpunch Active Member

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    Sep 29, 2019
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    Location:
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    Vehicle:
    2017 Prius v wagon
    Model:
    Four
    Weird. The little arc was probably just from dome lights, but since this behavior coincided with your battery replacement, couldn't hurt to disconnect battery, wait 10 minutes or so, then reconnect and see if that fixes it.
     
    #2 Centerpunch, Dec 2, 2019
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Vehicle:
    2010 Prius
    Model:
    Touring
    Not sure how much of a factor it might be, but I've always heard to disconnect negative first, and reconnect it last.
     
    #3 Mendel Leisk, Dec 2, 2019
  4. Centerpunch

    Centerpunch Active Member

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    2017 Prius v wagon
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    Four
    You disconnect the ground first because if your wrench accidentally touches a metal part of the car, there won't be a dangerous short created. (If you disconnect the positive first and your wrench touches the car, watch out!)

    Electrically it doesn't matter which you disconnect first. Power to the car is either connected or it is not.
     
    #4 Centerpunch, Dec 3, 2019
    Leadfoot J. McCoalroller and Mendel Leisk like this.
  5. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
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    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Yeah, that was it. I recall once installing both terminals loosely (on a jump pack battery). I then proceeded to tighten each, with a wrench: started with the positive terminal. The tip of the wrench handle touched a wire running back to the negative post: there was a big pop, puff of smoke, and a melted wire. :eek:

    Moral of the story: deal completely with one terminal at a time, and best to make negative first off and last on.

    Jumper cables are similar. I sometimes think it would be good if jumper cables were not connected to each other at all, just two separate cables. Start with the positive cable, get it connected both ends, don't touch it any more. Then and only then get the negative cable.

    Too, it's cumbersome, but face-shield and gloves are a good idea. I have them, do goof off, but you only have one body.
     
    #5 Mendel Leisk, Dec 3, 2019
    Last edited: Dec 3, 2019
    Centerpunch likes this.
  6. sam spade 2

    sam spade 2 Senior Member

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    Location:
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    Vehicle:
    2017 Prius c
    Model:
    Four
    Which MPG indicator are you watching ?
    Mine has several but it's a C.
    If that one is restable, reset it and see if things settle down.
     
    #6 sam spade 2, Dec 3, 2019
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