Slow Smart Key

Discussion in 'Gen 2 Prius Main Forum' started by qmanqman, Jul 21, 2025.

  1. qmanqman

    qmanqman Active Member

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    The unlock feature of my smart key is becoming slower and slower. This morning I had to pull on the door handle 3 times before the door finally unlocked. For a second I thought I didn't have my key on me. Is this a sign the battery is wearing out in the key fob?
     
  2. dolj

    dolj Senior Member

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    Could be. If you test the fob battery with a voltmeter, replace it if it is under 3 volts.
     
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  3. Mendel Leisk

    Mendel Leisk MMX GEN III

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    When I'm replacing I've found the outgoing batteries still display quite good voltage, over 3.0 volts. but they are crapping out.
     
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  4. bisco

    bisco cookie crumbler

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    fob key, 12 volt, lock motor, in that order
     
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  5. qmanqman

    qmanqman Active Member

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    OK so on our other Prius it must be the lock motor. Neither battery fob will open the doors and the 12 volt holds steady a 13.8V. Found this diagram on the interweb. Also found a Reddit that says the "Room Oscillator" is not where this diagram says it is.

    1. If it's one of the oscillator's how do you know and how do you know which one?
    2. Is it safe to assume replacing one also means the system has to be reprogrammed?
    3. What is the purpose of the "Security Indicator Light" to this system?
    [​IMG]
     
    #5 qmanqman, Jul 29, 2025 at 11:33 AM
    Last edited: Jul 29, 2025 at 11:50 AM
  6. bisco

    bisco cookie crumbler

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    don't test the 12 volt with the car on. test it with the car off. best to get a free load test at most auto parts stores, or buy a load tester100-amp-612v-battery-load-tester-61747.html

    same thing with fob batteries. without a load, they can read nominal 3.3 volts.
    if more than one door won't unlock, it isn't likely the actuators
     
  7. qmanqman

    qmanqman Active Member

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    Tested 12 V with car off and white clip unplugged. I might have the voltage wrong but it was solid and strong and this issue with the doors has been happening for a couple years now.
    Good to know. Didn't test that out. Can the fob itself wear out? Her fobs are pretty beat up.
     
  8. bisco

    bisco cookie crumbler

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    not really. you can try cleaning the inside and making sure the battery is tight. generally speaking, if the red light flashes when you press a button, it is working