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Smart Key not working

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by DC773, May 13, 2017.

  1. DC773

    DC773 Junior Member

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    I'm having an issue with my smart key unlocking the doors. Forgive me if this has been addressed elsewhere, but I've searched this site (and the web) and found no matches.

    I have a 2010 Prius, ~75k miles. The issue is 2 or 3 times out of 10, when locked, the car doesn't seem to sense my key. I have to push the unlock button on the key to open the doors. The other 7 or 8 times out of 10 it works fine, which is to say I approach the driver/passenger/hatch door with key in pocket and the car unlocks upon touch.

    There has never been an issue with starting the car. The key is always sensed then. Also, replacing the battery in the key solved nothing, and this happens with both keys.

    (One other thing I just noticed, which may be related, is I left the headlights on recently and they did not shut off automatically. I returned to the car ~15 minutes later and the lights were still on. Doors were locked, and I had to push key button to unlock. So the car didn't sense the key, and maybe it also didn't know to sense I was gone and it should turn off lights [?]. May not be related...)

    Does anyone have any thoughts as to the cause of this? Or any suggestions for a solution? Any help is greatly appreciated. I saw a couple posts related to Gen 2 issues similar (but not the same) to this, but they didn't seem to apply.

    David
     
  2. JC91006

    JC91006 Senior Member

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    Key fob battery issue?
     
  3. DC773

    DC773 Junior Member

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    Battery is fine, plus it's an issue with both keys—i.e. it seems to be an issue with the car, not the keys.
     
  4. JC91006

    JC91006 Senior Member

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    Key fob battery issue (bad replacements) or possibly 12v battery issue? If your 12v battery is original, change that first and see if things improve
     
  5. DavidA

    DavidA Prius owner since July 2009

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    The 12 volt. Mine did that before the 12v died completely. I was going through the fob batteries every 6 mos. thinking it was those and it wasn't. The dealer may say the 12 volt is testing fine. If 5+ years old, replace it no matter what the results of the test.
     
  6. WilDavis

    WilDavis Senior Member

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    12V AuxBattery might be starting to fail. Classic symptoms! Good luck!
     
  7. WilDavis

    WilDavis Senior Member

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    12V AuxBattery might be starting to fail. Classic symptoms! Good luck
     
  8. DC773

    DC773 Junior Member

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    I actually replaced the 12V battery about a year ago. A yellow Optima, bought new from NAPA. But since everyone is suggesting this same thing, I went and checked via this method:

    Check Prius Battery | PriusChat

    and I measured 8.4 V. Car has been sitting overnight. Is that right?! Isn't that so low that it wouldn't work at all? I thought it should be 12.x V.
     
  9. bisco

    bisco cookie crumbler

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    welcome!
    that's way low. did you leave a light on or door ajar? maybe there's an issue with the headlight timer.
    i'm surprised she makes ready. charge her up and see how she holds.
     
  10. DC773

    DC773 Junior Member

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    Thanks bisco.

    After some driving I checked voltage again, and got readings 12.6-12.8 V. I'll continue to take readings. The question is: if the battery continues to drain during non-use, what could be doing that? As best I can tell, no lights (inside or out) are ever left on.
     
  11. Former Member 68813

    Former Member 68813 Senior Member

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  12. DC773

    DC773 Junior Member

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    Can this be done with a voltmeter? And are you saying while the engine is running a healthy battery should show 12.x V? Thanks
     
  13. Sam Spade

    Sam Spade Senior Member

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    Or 12 V battery problem in the vehicle.

    Could be a failing door lock actuator too......in which case there probably would be a click or clunk and one door will unlock but not all of them.
     
  14. Former Member 68813

    Former Member 68813 Senior Member

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    yes, but under a significant load, lets say headlights on. measure the voltage with car off, but headlights on and post the voltage. i can give you my reading with my old and tired (nearly 7 years), but still good battery, and we can compare the numbers.
     
  15. Sam Spade

    Sam Spade Senior Member

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    "Nothing" is a big word. It can tell you SOMETHING.......like whether or not it has really been charging, whether it has been accepting a charge or if there is a substantial parasitic draw.

    Additional testing is necessary in any case.
     
  16. Former Member 68813

    Former Member 68813 Senior Member

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    if you measure it right after charging, it will not tell you if parasitic draw (takes time to deplete the battery) or how well the battery accepts charge (even badly sulfated battery will read fine on a surface charge). of course it will tell you that either battery is discharged, or totally bricked, or has one or more cells shorted. that's more then nothing, but it's barely anything.
     
  17. DC773

    DC773 Junior Member

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    Thanks, I'll take you up on that offer! I registered 12.8 V with all off. Then with just headlights on, 12.3 V.
     
  18. Former Member 68813

    Former Member 68813 Senior Member

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    your battery is better than mine. I got 12.7 and 12.0V.
     
  19. DC773

    DC773 Junior Member

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    Thanks ...does that leave me at 12V battery is fine? I.e. back to square one with key sensing issue?
     
  20. Sam Spade

    Sam Spade Senior Member

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    Maybe. Let it sit overnight and check it again.