2am and Car Alarm going off nonstop. Horn fuse?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by AlohaSpirit, Apr 7, 2019.

  1. AlohaSpirit

    AlohaSpirit Junior Member

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    2007 Prius. 100k miles. Recently replaced 12v battery.

    First time this has ever happened:


    Get home. Lock car... then alarm starts going off over an hour later.

    Turn off alarm via fob.... make sure all doors are shut properly... but it turns on about a minute later.

    Turn off alarm and it goes off 10 seconds later

    Then it starts going off almost immediately after. NONSTOP even with alarm "off" and door open.

    I get in and start the car... to prevent more occurrences then jump online to look for a fix.

    I pull the horn fuse. Does the 10a horn fuse run anything else i need to know about?

    From forum searches it could be.

    1. 12v battery (mine has been changed)

    2. Worn fob/battery in fob. (Recently replaced batter but fob is definitely old and weathered. No red light on either)

    3. Door switches.


    It's really early in the morning and I know this quiet neighborhood has been disturbed enough. So far it's been 15 min and no lights are going off (horn fuse pulled) but I'll be sleeping on the couch near the window to be by the car.

    If anyone has any insight, please share. I will be investigating both key fobs in the morning.

    Thank you very much
     
  2. RRxing

    RRxing Senior Member

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    Stuck panic button on the fob? Open it up as if changing the battery and close it back up again.
     
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  3. AlohaSpirit

    AlohaSpirit Junior Member

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    Horn went off despite horn fuse being out?

    Is the horn fuse purely for the steering wheel horn and not for alarm horn?

    Guess that's why I slept on the couch... :cry:


    Took battery out of old fob for now
     
    #3 AlohaSpirit, Apr 7, 2019
    Last edited: Apr 7, 2019
  4. AlohaSpirit

    AlohaSpirit Junior Member

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    I also recently changed the battery in the fob
     
  5. Mendel Leisk

    Mendel Leisk Denizen of the LZ

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    Disconnect 12 volt neg cable, take battery out of fob, reconnect 12 volt battery, see what happens?
     
  6. TMR-JWAP

    TMR-JWAP Senior Member

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    We've had this happen on 2 of the 4 Gen 2s that we've had in the family. Each time it was solved by pulling the fob battery out and using the spare fob. We then replaced the fob case, cleaned the circuit board and installed new battery in the previous fob.. The suspect fobs had holes worn in the buttons and we think dirt/dust had gotten in them causing the buttons to be sticky.
     
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  7. AlohaSpirit

    AlohaSpirit Junior Member

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    Thanks, I'm looking into the fob replacement now.

    My fob is pretty bad.
    2 button covers are gone.

    Still surprised that the horn went off
    (Even though fuse was pulled)
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Is it possible that the alarm is aftermarket and is triggering an auxiliary horn (and not the horns located in front of the radiator)?
     
  9. AlohaSpirit

    AlohaSpirit Junior Member

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    I'm not sure but I can try check
     
  10. RobertK

    RobertK Member

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    You don't need to replace the entire fob if the buttons are worn. You can buy a new fob case and transfer the guts from the old case to the new one without the need for any programming. The case costs about $13-14 bucks and is easy to change. I bought mine on Amazon and it works fine. The only differences I saw were that the new case had a matte finish instead of gloss and there was no Toyota logo on the back of the new case. I used my old back with the logo and it fit perfectly.
     
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  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Do not forget to transfer the RFID chip if the case is replaced.
     
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  12. AlohaSpirit

    AlohaSpirit Junior Member

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    I bought the fob case, which should be here in a week.

    Went off again at the end of work.

    Naturally it only happens w in range to your failing fob. Removed batteries when I got home.
     
  13. AlohaSpirit

    AlohaSpirit Junior Member

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    Switched over the electronics w the $10 replacement and everything seems to work fine. Not sure if it'll solve my alarm issue so we'll see.


    *Watched a few videos and since there has been problems from prying (and damaging) the circuit board, I released it from the fob by pushing from the button side.

    [​IMG]
     

    Attached Files:

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  14. AlohaSpirit

    AlohaSpirit Junior Member

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    Ok. Problem still persists.
    But at least it's daytime.

    I even replaced the fob battery just in case.
    When the panic sounds, the red light of the bad fob flashes and I'm unable to turn it off w the bad fob.

    What works is when I remove the battery from the bad fob and deactivate with the good fob. Panic hasn't gone off that way either.
     
  15. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Is it possible for you to determine the location of the alarm horn and disconnect it?
     
  16. AlohaSpirit

    AlohaSpirit Junior Member

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    That's next on my list

    Although I still run the risk of draining my battery when the lights go off

    Seems I have to disable the panic button somehow
     
  17. dolj

    dolj Senior Member

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    Did you give the circuit board, particularly the contacts of the switches, a good cleaning with PCB or contact cleaner? If not that might be worth a try.
     
  18. AlohaSpirit

    AlohaSpirit Junior Member

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    I did not. That's another thing to try.
     
  19. AlohaSpirit

    AlohaSpirit Junior Member

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    So I retired the other fob since it continued to happen and switched to my other fob.

    Started happening again today. Will check battery as #1. (I guess this is the default whenever your fob battery goes)
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

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    See if the fob button is stuck in the depressed position; that happened to one of my 2007’s fobs.
     
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