w124 drivers door unlock alarm goes off
 

Hi guys I have a strange issue...

Whenever I unlock the drivers door and then open the door thr alarm goes off. If I unlock from passenger side it's fine.

Also if I unlock from drivers side and wait about 20sec it's fine too...

Any ideas where to look?

Yep, look under floor cover on passenger side front. You will see module there. I run with mine disconnected.

I would like to fix the issue, not remove the issue.

Where can I look first to figure out why its happening?

To re-iterate...

Drivers door = Alarm goes off
Passenger Door = works normal
Trunk = works normal

So why would just the drivers door cause the alarm to trigger? I don't think this is a module issue otherwise all the doors would cause the alarm to trigger since its vacuum operated.

sounds like poor contacts in the driver door key lock tumbler

So are you saying new door tumbler unit?
I don't believe its too expensive, so I am not opposed. I think it was $50 for the lock + key a few years ago...so not far off today.

I have had this with two 124's...intermittent problem....

perhaps, switch tumblers from passenger to driver....

me, I just lived with it.....

The switch by itself is $130.

Does the tumbler unit come with the switch if I buy it complete?

I've had my alarm go off twice. First time was when I locked it while the passenger door was ajar. Took me while to get it to stop and I honestly don't recall how I did it. The other time was last summer. I unlocked the door, opened it and the alarm went off. I tried a few things while the car was running (lock & unlock the door from inside) or not. Finally got out and locked and unlocked the door with the door open and closed. I think it stopped when the door was closed. Anyway, it stopped and hasn't gone off since.
In all honesty, however, I rarely lock the car. ;)

well,
I don't want to sound smart, but it could as well be the alarm module.
The door contacts are open when the door is closed. Once opened the contact closes a circuit to chassis ground.
The switch therefore does not sound to be the culprit. If bad, it wouldn't make contact to chassis, no alarm trigger.
It is my understanding that the alarm module, senses the door contacts and a certain condition has to exist in order to trigger an alarm. All of this maybe inside the alarm module...
I can't remember where the module is located at, but have a vage memory somewhere, perhaps the underhood relay box.

Good luck!

P.S.
There should be a momentary switch under the hood driver side. If I am not mistaken this is the Alarm Override switch.
The alarm should go off once pushed. If not, then the alarm module has a problem.
I have found serious solder / contact problems in many of the modules used in those vehicle. They were designed, in my opinion, to last perhaps 10 years, since most Mercedes first owners would get rid of the vehicle on or before anyway.
The problem posted, may as well be, again, just a solder / contact problem.....

The alarm module should be located under the front passenger side foot-rest floor plate.

^^^^^ This..

Just disconnect it too. Nobody is stealing W124s these days, they aren't hot on anyone's list.

He explicitly said he wants to maintain this functionality. Though personally I have disconnected the alarm on my 560SEC (basically same module) after it started malfunctioning back in 2006. The module on my 1994 E500 is still working but I'll probably disable it too, at some point....

FWIW, I had a customer in the UK want his alarm fixed. He said his was not working correctly and that there was no replacements available. He mailed me the unit and I re-flowed/re-capped the unit. I didn't have a way to test it so I sent it back to him. He reported that it was working normally.

This leads me to believe that maybe there is something that could/might go wrong in the alarm unit. It should be added to the list of suspects, perhaps.

Just would be interesting to know, how much did that cost?

I just checked my emails, I only charged him $40 for the parts+labor.

Here is what the alarm unit looks like inside, at least the W126 euro/UK variant
W126 Becker Alarm Module - Imgur