W202 alarm goes off randomly

[AK84]

Hi everyone!

I have a '96 W202 C180 Mercedes. I bought it last year on november. It has a factory alarm unit (there is a button in the console with a red light in the middle - see attached pic). When I bought it there were no problems. Lately the alarm has started going off for no apparent reason. Sometimes three or four times a day. It's very frustrating because it occurs in the evening too and I'm having a lot of complaints from the neighbours who can't sleep. I tryed with switching off and on the button on the console, but no luck (before it could be switched off). The light still flashed after I locked the car. If I press the upper part of the button the light light up and stays lit for about 2 sec. If I press the lower part then it flashes rapidly and repeatedly for 2-3 sec. When is it on and when is it off?

I want at least to disconnect the wire which triggers the car horn. So everyone can sleep... But I can't find where it is. Can somebody help me with a guide please (better if it has pictures too)?

What I did today was open the trunk and near the battery there is a fuse box. And I removed fuse no3. which is for the anti theft alarm. Now the red light in the console doesn't blink anymore. Even if I pres it. I hope this manner the alarm won't sound anymore. Could this harm the car?

Sorry for my english :]

 

[stevesey]

Ditto - see my posts earlier in the week (I was reading my manual at 1:00am on Thursday).

Press top of button to disable the tilt/tow away sensor, bottom to disable the interior sensors. If you want to disable both press one, wait for the LED to stop doing it's stuff and press the other - then get out and lock the car.

N.B. You need to repeat the procedure each time you lock the car (it's only disables the sensors until the car is unlocked when they are re-enabled).

During the day at the moment I'm trying one and then the other to see which (if either) is the cuplit (but then turning them both off overnight). Of course at the monent sod's law prevails and it's behaving itself.

 

[AK84]

Thanks for the reply stevesey! For now I've taken out the fuse and till now no probs. Will try to put it back tomorrow and try to disable the alarms with the button as you said. However I've tried it (pressing the button, than waiting till the light goes off and then pressing the lower part of the button) and when I lock the car the light on the button flashes. If I'm not mistaken it should not flash when disabled?

 

[stevesey]

If I'm not mistaken it should not flash when disabled?

Mine still flashes when you lock the car. I think that's normal as even with both sensors disabled the alarm is still active via the door switches.

 

[AK84]

I see. Will try it.

It's strange to see this alarm system in my car, because afaik it is only in facelift models, but mine isn't a facelift model. It should have been an optional extra I think...

 

[bouncer]

Had the same thing with my car for a while, got told to clean it out with the hoover!
Spider in the car, must have got it because all is fine, alarm only goes off now if i make it go off.

sTeVe

 

[AK84]

Interesting. But I don't think in my case an insect was the problem, cos when I want to I can't make it go off. So there must be a problem with the whole system. However I put out the fuse and since then no problems (I don't have alarm now, but it's stil better than having one which goes off twice a day...)

 

[vijilants]

Amazing that there isn't a way of permanently disabling the system from the switch.

 

[AK84]

Yeah would be better than taking out the fuse from the fuse box in the trunk... It's a pitty.

 

[ROBB]

i had something similar last year - turned out to be the alarm siren. the internal battery was kaput and kept triggering the flashing lights.
new siren fitted, STAR reset: done

 

[AK84]

Thanks for the info ROBB. Will look into that. The problem is computer test here in Hungary cost a fortune

 

[chord]

i had something similar last year - turned out to be the alarm siren. the internal battery was kaput and kept triggering the flashing lights.
new siren fitted, STAR reset: done

I called my local specialist and he said something similair, quoted around £150 to get the above done. Do you mind telling me how much it cost you.
Did you try all the suggestions in the other thread before getting the siren replaced?

 

[Wezzel]

My alarm goes off perodically and it is always an insect. Usually after taking garden refuse to the tip

 

[chord]

My alarm goes off perodically and it is always an insect. Usually after taking garden refuse to the tip

After disabling the internal sensors with the switch on the dash, my alarm has not gone off again. It appears insects are the most likely culprit...

 

[stevesey]

Similarly I have been disabling the internal sensors each night and all has been fine for the past two weeks. During the day/eve the alarm the sensors have been on and the alram hasn't gone off either. Need to bite the bullet now and try the sensors overnight, to see if it the "insects" have moved on.

 

[AK84]

Mine would go off even during the day. Must have been some freakin huge insect Anyway since I popped out the fuse, no more alarm, no more problems

 

[tambyrne]

Had the same problem with my C200 it was a midge sized fly. Spraying the interior with fly killer did the trick.

 

[normanr]

I had a 1999 C200 with the same problem and was told on a night when finished using the car to close the vents inside the car as a gust of wind going through the vents into the car can set the alarm off.

I tried this with my car and it stopped the problem I might add mine was going off sometimes at 2am.