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2004 Prius Possible Key Fob issues??

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by yzfrider2001, Mar 13, 2015.

  1. yzfrider2001

    yzfrider2001 Junior Member

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    Vehicle:
    2004 Prius
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    I replaced the battery (with a new Energizer) in my wife's 2004 Prius key fob a couple of months ago and it worked fine until yesterday. Now, the fob will unlock the doors it will not start the car. She said it stalled on the way home yesterday and the only way it would work is when she inserted it. Now, this morning, when she inserted the key the car would not start and the key light came on - but it still unlocked the doors. Any help would be greatly appreciated!
     
    #1 yzfrider2001, Mar 13, 2015
  2. Kurzweil

    Kurzweil Member

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    Location:
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    Vehicle:
    2010 Prius
    Model:
    III
    Do you have another FOB that works correctly? If so, the problem would appear to be within the key fob itself. When diagnosing such issues, I always look first in the area where I messed with it. The obvious first step is to try a new battery, or at least do a voltage check on the present battery. NEW does not guarantee GOOD.

    If the battery is not the issue, and since it will open the doors it appears to be OK, then the FOB may need to be replaced. I believe that the programming is in the car; not the FOB, so that should not have changed with battery replacement. Just the process of opening the unit could have sent a marginal connection over the edge. My best guess at this time.
     
    #2 Kurzweil, Mar 13, 2015
  3. TJ.Kabel

    TJ.Kabel New Member

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    Vehicle:
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    One
    I have the same problem but a new battery doesn't change anything. And since I was so proactive and changed the battery in both my fobs at the same time... now one will unlock the car but won't start it, and the other fob starts the car but won't unlock it! What do I do now?
     
    #3 TJ.Kabel, Mar 13, 2017
  4. Beachbummm

    Beachbummm Senior Member

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    the battery you installed may have been new but could have been almost dead from sitting in the store... Id start with two fresh batteries from another store ..
     
    #4 Beachbummm, Mar 13, 2017
  5. Sam Spade

    Sam Spade Senior Member

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    ALL of these symptoms are likely a combination of pure coincidence AND a dying 12 V aux. battery in the car.
    Get the 12 V battery tested.
    If it is over 5 years old, just replace it.......and then test the charging voltage while the car is "running".
     
    #5 Sam Spade, Mar 13, 2017
  6. christiw5

    christiw5 Junior Member

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    Location:
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    Vehicle:
    2006 Prius
    Model:
    II
    We had the same problem with daughters car at college. We had to get a new key and have it reprogrammed.

    Posted via the PriusChat mobile app.
     
    #6 christiw5, Mar 19, 2017
  7. christiw5

    christiw5 Junior Member

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    II
    Also you should know that when you reprogram a FOB it has to be programmed for both the start and the unlock process.

    Posted via the PriusChat mobile app.
     
    #7 christiw5, Mar 19, 2017
  8. archae86

    archae86 Member

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    Location:
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    Vehicle:
    2006 Prius
    We have a 2006 Prius. When the original 12V battery got weak, a very early symptom was some oddity in key fob recognition and such.

    A general them on 12V battery weakness is that symptoms seem to vary from car to car (or at least owner to owner, we don't all notice the same things or report them the same way).

    All things considered it may more likely be a fob issue, but keep the 12V possibility in mind. And if the 12V has more than four years on it, I'd seriously suggest you consider replacing it pre-emptively.
     
    #8 archae86, Mar 20, 2017
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