Driver's door lock not disarming alarm - PeachParts Mercedes-Benz Forum

smharr4 · #1 07-10-2010, 02:54 AM

My 1993 300E2.8 has developed a strange problem. Unlocking the driver's side door from the outside with the key unlocks all the other locks (including trunk and fuel filler flap) but will not disarm the alarm, and I have to walk around to the passenger side to unlock that door to disarm it.

This used to be just a winter problem which went away with the warmer weather, but it's continued into the summer this year and is getting really old.

Plus, the driver's door doesn't unlock when I unlock the passenger door (but the alarm is disarmed.) This means that I'm always making at least one trip around the car to open all the doors and turn off the alarm, unless I reach in and lift the driver's door lock stalk.

Does anyone have any idea as to what's going on?

Jer · #2 07-10-2010, 08:08 AM

In regards to the alarm, there are microswitches clipped to the lock cylinders of the two front doors. Turning the key causes a cam to flip the microswitch in either the arm or disarm position (depending on which way the key is turned). These are momentary contacts. Depending on the part # of the cylinder, you might be able to order a replacement switch. In some cases you have to order the whole lock cylinder with switch, which costs more. The same problem happened with my '94 E320.

For now you can pull out the plastic cap inside the door above the latch and disconnect the 3-pole plug for the ATA microswitch. This will prevent the alarm from being armed when you lock the door.

As for the driver door not unlocking, check for vacuum leaks from the central locking pump to the driver door lock vacuum element.

mlozzi200478 · #3 07-10-2010, 10:55 PM

thanks for the ideas,im having the same issue with my 89 300ce,left door doesnt operate central locking system,and the alarm does not arm,or go off no matter wich door is locked,then opened from the inside while locked,maybe i need to replace both micro switches,and find the vacum leak.

smharr4 · #4 07-13-2010, 09:57 AM

Could the microswitches just need lubrication, and that's why they worked in summer but not in winter?

Jer · #5 07-13-2010, 11:51 AM

Lubrication won't help. The switch is sealed with a rubber boot. The switch will move but not enough for it to click, which you can hear when it does.