Why does my key fob not work first thing in morning?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Joe Wall, Aug 15, 2021.

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  1. Joe Wall

    Joe Wall Member

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    After working out within range my key fob wont unlock. It is always the first time i use it in the morning. I try unlock and lock at least 10-20 times then use the manual key. The rest of day it works just baffles me why this is occuring.
     
    #1 Joe Wall, Aug 15, 2021
  2. dolj

    dolj Senior Member

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    How is the CR2032 button battery in the fob?

    What is the voltage of the 12 V battery in the right rear first thing in the morning?
     
    #2 dolj, Aug 15, 2021
  3. archae86

    archae86 Member

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    When the original 12V battery in our Prius began to age, fob reception problems were one of the symptoms. The fact you are seeing trouble first thing in the morning somewhat fits a 12 V problem, as overnight the battery voltage will have dropped down a bit.

    If that is really the case, probably things will get worse when it gets colder.
     
    #3 archae86, Aug 15, 2021
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  4. Joe Wall

    Joe Wall Member

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    Ill check the voltage in the morning and let you know. Thanks!
     
    #4 Joe Wall, Aug 15, 2021
  5. Joe Wall

    Joe Wall Member

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    I bought it used and had something dine with 12v battery. Id have to check the service history when get home.
     
    #5 Joe Wall, Aug 15, 2021
  6. ColoradoBoo

    ColoradoBoo Senior Member

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    When you walk up to the car with the fob, does the red light on the fob come on? This indicates that the fob detects the car and is active so if the red light does come on, it's a problem with the car system, not the fob.
    How old is the 12 volt battery? I've heard that many (most?) strange electrical problems start with the 12-volt battery going out.
     
    #6 ColoradoBoo, Aug 15, 2021
  7. Joe Wall

    Joe Wall Member

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    The lights showing mph and etc dim out if i keep lights on as well. Then i turn them off. Think the dimming if from battery as you mentioned
     
    #7 Joe Wall, Aug 15, 2021
  8. fuzzy1

    fuzzy1 Senior Member

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    This part should have nothing to do with the battery, if you are testing while the car is READY and running. When READY, the 12V system is powered and regulated by an inverter from the traction battery. This is the Prius version of the alternator & voltage regulator of a traditional car.

    There is a scroll wheel brightness adjustment to control if, and how much, the dashboard lights dim at night when the headlights are turned on. If you don't want them to dim, e.g. when using the headlights in daytime, roll that adjustment wheel all the way up, then 'clicks'.
     
    #8 fuzzy1, Aug 15, 2021
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  9. edthefox5

    edthefox5 Senior Member

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    Measure the 12 volt battery with engine off first thing in the am before starting the car.

    Measure it at the front jump under the hood with car off. It is useless to measure it directly.

    If your not close friends with the 12 it probably has a corroded ground connection too. This can be detected by measuring at the front jump point. Then measure directly at the battery. If more than exactly .5 volts less at front JP there is a connection/corrosion issue in the hatch.

    12 volt battery is probably sitting in water too. Very leaky back there.
     
    #9 edthefox5, Aug 15, 2021
  10. bisco

    bisco cookie crumbler

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    post #3 nailed it
     
    #10 bisco, Aug 15, 2021
  11. Joe Wall

    Joe Wall Member

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    Red light does come on
     
    #11 Joe Wall, Aug 16, 2021
  12. bisco

    bisco cookie crumbler

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    what was the 12v reading?

    how old is it?
     
    #12 bisco, Aug 16, 2021
  13. Joe Wall

    Joe Wall Member

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    Will get reading tmrw or next day
     
    #13 Joe Wall, Aug 17, 2021
  14. Joe Wall

    Joe Wall Member

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    Gonna do a load test today and can test tmrw morning
     
    #14 Joe Wall, Aug 17, 2021
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  15. Joe Wall

    Joe Wall Member

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    Weird load test says 100%.
     
    #15 Joe Wall, Aug 17, 2021
  16. Joe Wall

    Joe Wall Member

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    Red light was on tho ocassionally
     
    #16 Joe Wall, Aug 17, 2021
  17. Joe Wall

    Joe Wall Member

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    Key fob was dead lol.
     
    #17 Joe Wall, Aug 17, 2021
  18. bisco

    bisco cookie crumbler

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    was that the problem?

    what load tester? did it show voltages?
     
    #18 bisco, Aug 17, 2021
  19. bisco

    bisco cookie crumbler

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    does it?
     
    #19 bisco, Aug 17, 2021
  20. Joe Wall

    Joe Wall Member

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    Fob key battery was dead. Load test was 100% for battety. Kind of a pain to access the battery.
     
    #20 Joe Wall, Aug 17, 2021
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