1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Alarm comes on randomly

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by SlimJim, Feb 22, 2012.

  1. SlimJim

    SlimJim Member

    Messages:
    21
    Likes Received:
    0
    Joined:
    Jul 31, 2011
    Location:
    Edinburgh
    Your Mercedes:
    '04 E220 CDI Estate
    Hi Folks,

    I'd appreciate some advice on a fault with the alarm on my 97 P reg pre-facelift W202.

    Yesterday evening the alarm on my car started going off seemingly at random. It started immediately after I arrived home from work and then whenever I relocked the car with the key fob the alarm would go off between 5 and 10 minutes later.

    I looked at the obvious things checking doors were locked etc and I disabled the interior sensors and tow-away alarm. I thought that had sorted the problem, but then about 11:30 the alarm went off again!

    This morning after I arrived at work I was told by a friendly email that my car's alarm had gone off, but by the time I got to the car (about 10mins later) the alarm had gone off and it behaved itself for the rest of the day. That is until half an hour ago! I've disabled the interior sensors and the tow-away alarm again but I'm not optimistic.

    I'm not sure if this is relevant, but when I got into the car to leave work today and started the ignition I noticed that the red led in the mirror was flashing slowly for about a minute. I'd not seen that before. And again this evening after the alarm had gone off I noticed the same slow red flash when I put the keys in the ignition.

    Any ideas what I can do or what the cause might be? Is there a way to switch the alarm of but keep the remote central locking working?

    Thanks,

    SlimJim.
     
  2. grahamcol

    grahamcol Senior Member

    Messages:
    1,503
    Likes Received:
    336
    Joined:
    Jan 12, 2009
    Location:
    West Midlands
    Your Mercedes:
    2001 SLK230, 2007 CLK220 CDI
    Might be the alarm siren. Try unplugging it. That said, it's usually the facelift ones that tend to play up. Those ones are located behind the n/s/f wing splash guard and the internal batteries tend to go kaput.
     
  3. william28ho

    william28ho Active Member

    Messages:
    40
    Likes Received:
    0
    Joined:
    Apr 21, 2010
    hi - have you check the car's battery? because a low (power) battery does gives a wrong signal to the car's alarm.

    a normal new car battery only has about 4 years life span.


    i hope this has help
     
  4. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    319
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    I would think the siren has expired, they can have internal re chargeable batteries, un plug it and see if the alarm still goes off
     
  5. OP
    SlimJim

    SlimJim Member

    Messages:
    21
    Likes Received:
    0
    Joined:
    Jul 31, 2011
    Location:
    Edinburgh
    Your Mercedes:
    '04 E220 CDI Estate
    Latest development is that the car no longer beeps when I open and close it although everything else works fine and the indicator lights still flash.

    Does indeed look like the siren has failed...
     
  6. OP
    SlimJim

    SlimJim Member

    Messages:
    21
    Likes Received:
    0
    Joined:
    Jul 31, 2011
    Location:
    Edinburgh
    Your Mercedes:
    '04 E220 CDI Estate
    Of course that would be too simple. :mad:

    I assumed that the siren had failed but no the problem came back today exactly as before. It would seem the siren is working (and as loud as ever) - although the central locking does not beep when locking and unlocking the car.

    Could it still be the siren or should I look elsewhere?
     
  7. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    319
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    You must unplug the siren and see if the alarm still goes off by looking at the flashers. they are wired into the CAN bus and can upset the whole system
     
  8. star

    star Forum Supporter Authorised Forum Supporter

    Messages:
    5,629
    Likes Received:
    1,080
    Joined:
    Oct 6, 2004
    Location:
    Reading
    Your Mercedes:
    Smart + others :)
    Get it read to see whats activating the alarm.
     
  9. WG M-B

    WG M-B Senior Member Authorised Forum Supporter

    Messages:
    3,105
    Likes Received:
    6
    Joined:
    Dec 5, 2010
    Location:
    North west london
    Your Mercedes:
    C63 Wagon in black
    As star says. It's most likely the alarm siren but other usual suspects are the interior motion sensors, and the towing sensor. If interior lights are going out then I suspect no fault with the door switches
     

Share This Page