Alarm going off intermitently when not armed, even with doors open! Help!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by SamM, Mar 25, 2014.

  1. SamM

    SamM Junior Member

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    I have an 04 Prius with 80k miles. It recently had an HV battery rebuild due to a bad cell. That was fixed and seems fine. It had a P0A80 code and that's now gone.
    Now the alarm is going off repeatedly at odd times. The alarm is not armed and it still goes off. No dash error lights are lit. The door or hatch can already be open, sitting for a while, and the alarm will still actuate. I pulled the horn fuse to avoid aggravating the entire neighborhood but the lights still flash with the now-muted alarm. Now i need to disconnect the negative battery lead to save the battery and lights at night.
    The key fobs are fine. I keep them far from the car.They work properly.
    I tried turning off the smart key function under the dash with the on/off button. No help.
    I replaced the 12V battery with a new one. No help.
    I tried locking the car with the fob. No help
    I tried leaving the car unlocked with the fob. No help (If you unlock with the fob the car will auto-lock anyway)
    I tried not using the fob but leaving the doors unlocked by manually using the locking mechanism on the door to be sure not to arm the alarm. no help.
    I tried unlocking the car, then opening the door manually and closing it while unlocked so the door will stay unlocked and not autolock. No help.
    The panic button works properly. The key fob battery is fine. The 12V battery voltage is good with and without load.
    I don't trust my local dealer to properly diagnose or honestly fix this so I'm at a loss!
    Any advice would be greatly appreciated.
    I would prefer to just disconnect the alarm but from my reading of other threads, that seems to not be an option. I don't need an alarm. I just need my reliable car. Up til now, this car has been awesome.
    Thanks!
     
    #1 SamM, Mar 25, 2014
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Does the car have an aftermarket alarm? If yes, that should be disconnected.
    2. If the car only has the factory alarm system, then the most likely cause of a false alarm is that there is a problem with a door or hatch switch.
    3. In order for you to DIY, you need to access repair manual info at techinfo.toyota.com and you also will need Mini VCI (Toyota Techstream clone which runs on a Windows XP or Windows 7 32 bit OS laptop) in order to see the state of the system.
    4. One alarm function in particular is called "passive mode" and that should be turned off for your system. That may be part of the problem, where the system arms automatically after 30 seconds after the fob is removed from the slot, even if the doors are left unlocked.
     
    #2 Patrick Wong, Mar 25, 2014
  3. SamM

    SamM Junior Member

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    Thanks for the advice Patrick! It is a factory alarm and the car is totally stock.
    I'll see about getting the Mini VCI and asap get some codes. My OBD2 reader is not showing any errors. I'll post anything I find on this thread. I'm sure that others have the same problem. They probably end up going to the dealer and hope not to get gouged too badly.
    It was weird because today the alarm sounded even before I got out of the car! I was in the drivers seat with the door open and it went off. it will go off with and without doors open. It does not go off with the key fob mechanically stuck in the key slot, however. Of course, then my car can be stolen!
    I tried to deactivate the passive mode with the series of complicated switching of knobs and locks but was not successful yet.
    I'm hoping the the combo of converting to active mode and turning off the 'warn-by-horn' function will make it so I don't have to undo the battery every night!
    Thanks again.
     
    #3 SamM, Mar 25, 2014
  4. dorunron

    dorunron Senior Member

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    I know this sounds like grasping at straws, but I wonder what might happen if the orange service plug was reseated. Problem did not occur until after hybrid battery change.
     

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    #4 dorunron, Mar 25, 2014
  5. SamM

    SamM Junior Member

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    Tried reseating the orange service disconnect. No help. I am now getting dash error lights. Red triangle, VSC, and brake light.
    Took it to advance auto and they scanned it and said it was
    ERROR CODE C1310 malfunction in HV system.
    The car runs great and is getting 50+mpg
    I'm not able to find much info on this error code. Any ideas?
     
    #5 SamM, Mar 26, 2014
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    DTC C1310 is logged by the skid control ECU and means that there is a malfunction in the hybrid vehicle system. The hybrid vehicle ECU probably also logged a DTC that was not picked up by Advance Auto.

    If those warning lights appeared only after you reinstalled the orange service interlock switch, make sure that you slide the switch lever down to lock it in place, after pivoting the lever 90 degrees.

    If those warning lights persist after you've checked the interlock switch, it is time for you to seek professional assistance, ideally from a Toyota dealer whose service department you believe to be competent.

    Or, subscribe to techinfo.toyota.com so that you can research the DTC and decide if you can do something about that.
     
    #6 Patrick Wong, Mar 26, 2014
  7. freesky

    freesky Junior Member

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    Anyone have info on how to access the body module computer plug? I need to re-seat mine to fix similar false alarm issues like SamM has.
     
    #7 freesky, Mar 26, 2014
  8. SamM

    SamM Junior Member

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    UPDATE:
    Well, it appears that the second Key FOB was to blame. I never use it and it has been sitting in a drawer for years. It was far away from the car with several brick walls intervening, but I found that the red LED on the second key fob was blinking. I removed the battery from the second key fob and the car has not alarmed since (one week).
    I assume that the small battery in the second key fob was dying and somehow intermittently triggering the panic alarm on the car. That would explain why it happened when the doors were open or closed, armed or unarmed.
    At least that's what I think!
    So always check both key fobs any time you have an alarm problem, and it's best to just store the second key fob with the battery removed!
    Thanks for all the help and comments.
     
    #8 SamM, Apr 4, 2014
  9. nh7o

    nh7o Off grid since 1980

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    Glad that it looks like you found the problem. Note that brick is fairly transparent to VHF radio waves, so it looks like "far" was not really far enough. I always press the "Key" switch under the dash when the car is not in use.
     
    #9 nh7o, Apr 4, 2014
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