Alarm comes on randomly

[SlimJim]

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.

 

[grahamcol]

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.

 

[william28ho]

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

 

[television]

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

 

[SlimJim]

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...

 

[SlimJim]

Of course that would be too simple.

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?

 

[television]

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

 

[star]

Get it read to see whats activating the alarm.

 

[WG M-B]

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