2015 Prius C, horn blaring and doesn't stop when driving

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by 2722Kyle, Dec 11, 2025 at 10:52 PM.

  1. 2722Kyle

    2722Kyle New Member

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    Location:
    California, USA
    Vehicle:
    2015 Prius c
    Model:
    One
    Hello All,

    This is my first post here, but I am getting frustrated with my 2015 Prius C. Recently, I parked my car and went to lock it with the key fob (physical key) and when I locked the door the horn started blaring. Thought it was a door not being closed properly so checked that, checked door latches/switches no apparent issue there and eventually the horn/alarm stopped on its own. When I got back in the car no issue but when I got out and got back in again, upon unlocking the car the horn started again and this time it didn't stop even when driving and locking the car etc. I removed the fuse as a temp solution, got the car checked out and alarm disabled. Now my car alarm is finicky and the normal "chirp" when locking/unlocking isn't there and is replaced with the horn. Whenever I lock my car I hear "honk --- pause --- honk" and it takes two clicks of the unlock on the fob to unlock the car and sometimes the horn will start blaring doing this. Any ideas? I already changed key fob batteries and will be going to try a different fob and testing the 12V battery. This happened before a couple years ago and eventually the horn stopped working all together. Mechanics did something to the ECU and it fixed. Also, apparently I have an aftermarket alarm system. Car was pre-owned and sold by Toyota.
     
  2. 2722Kyle

    2722Kyle New Member

    Joined:
    Yesterday
    2
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    0
    Location:
    California, USA
    Vehicle:
    2015 Prius c
    Model:
    One
    Update: I have also noticed that my dashcam connected to the 12V cigarette lighter was taking several minutes longer to turn on. Could this be due to the P/I fuse being faulty or blown?
     
  3. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
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    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    I'd say check the dashcam's storage- it may be time to reformat the memory card, or if enough cells have gone bad it may be due for replacement. It's possible that the device is struggling to mount the storage at boot time, adding a variable delay to the start of recording.

    A missing or burnt out fuse on the circuit feeding the dashcam would prevent it from working at all. A problem with any other fuse would have zero effect. So, I think your dashcam issue is completely unrelated to the alarm problem. I don't have any particular advice for the alarm condition beyond hiring a pro to replace it or remove it altogether.

    Good luck!