when and how to replace FOB battery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by priusunum, Nov 11, 2012.

  1. priusunum

    priusunum priusunum

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    To check whether your FOB's battery is weak or needs replacing, push any of its buttons(but preferably not the panic button!): if a red light does not flash on the upper right corner, you need to replace the battery.
    To replace, purchase a CR 2032 round battery (sold in many drugstores). Then take out the mechanical key on the FOB by simultaneously pushing to the side the small slider and pulling out the key. Then (and this can be hard to do), simultaneously push the back panel toward the front with one thumb while at the same time pushing the slider to the side once more with your other thumb. You may have to try this several times before succeeding. Don't ty to use a screwdriver to pry off the back panel! With the back panel off, you need to unscrew four very, very tiny screws to get to the battery. This requires a very small screwdriver, such as one used for eye glasses or watches. When you have taken off the screws, remove the battery's cover and replace the battery. Then do everything again in reverse to close. Test the battery by pushing any button (but again better not push the red panic button): if the small red light flashes, you're good to go.

    I recently had to replace the battery on my spare FOB which I have never used (but decided to test) because it failed the red light test. And indeed when I went to my car with that FOB, it would not work to lock/unlock the doors. After replacing the battery, it did work. I replaced the battery on my other FOB a year ago and it's still working ok. I have a 2006 Prius.

    I'm writing all this to help others as I have been helped a number of times by reading this excellent website.
     
    #1 priusunum, Nov 11, 2012
  2. rcf@eventide.com

    [email protected] Member

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    I don't remember if the red light blinked or not, but I recently changed a fob battery after noting three symptoms:

    First, the car recognized me more slowly than usual.
    Next, I found that I had to press the fob button to unlock the door
    Finally, and most strangely, I had to hold the button down a few seconds to open the door.

    All of this progressed over a period of several days. When I took out the old battery, it measured about three volts. A new one typically reads 3-1/4V

    In other words, there is at least some warning that the battery should be changed well before it dies completely.

    Richard
     
    #2 [email protected], Nov 11, 2012
  3. maestro8

    maestro8 Nouveau Member

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    I bought my battery at the dealership, and they replaced it for me at no cost. I was prompted by the same symptoms, namely the car not unlocking without a fob button press.
     
    #3 maestro8, Nov 12, 2012
  4. archae86

    archae86 Member

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    As it happens I saw this post this morning just before I went to work on my wife's fob. I'll add some comments.

    1. ours is 2006 Prius with SKS. There is no little red light to check on these.
    2. a symptom you can add to your list is that the fob gets you in the door when it is warm from being in your pocket but not when it is chilled from sitting in the bottom of your wife's knitting carry-all on a cold morning ride to church.
    3. The (fluke) measured voltages on our "bad batteries" were about 3.002, while the not quite fresh batteries from my drawer stock measure 3.28.
    4. I drive the Prius once in a blue moon, while it is my wife's daily driver. But she never pushes the fob buttons, so it seems they drain their batteries at the same rate, as the measured voltages matched within a few millivolts.

    I can't recall whether I already replaced these once, so don't know whether we are getting three year life or six year life.
     
    #4 archae86, Nov 12, 2012
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