My car unlocks itself
 

While driving or when the car is parked. My '92 400E unlocks all the locks even, when I have parked it and locked it. I come back to see it unlocked. It also happens about 10 or more times while I am driving. Any ideas how to remedy this? Where is the control unit (electrical) to lock the doors. I am assuming it is electrical even, though the locs unlock by vacuum. I had the fuel door and trunk actuators replaced about a 1 and 1/2 yrs ago when, they were leaking. Checked both. I was going to check doors but, couldn't take it off. Dealer did door strap mod and I think they glued the inside door panels. It seems that way unlike, my 560 SEL which, just had snap pins and screws holding it down.

I forgot to add that I have cleaned the inside keyhole with electric contact cleaner and lubricated all locks with a spray lubricant not, WD-40-similar though. I have also stripped the trunk and tried to look for the vacuum pump for the locks but, was unable to find it. All my doors, trunk, and fuel door lock and unlock but, this random unlocking of every door is ridiculous. Help!

I'm pretty sure you'll find the vacuum pump underneath the rear seat bench.

From there, you could connect up a meter and monitor the readings..

Will try that.
Thanks

I am having a similar problem on my 300TE... shop replaced the pump, and yes it is under the right back bench, but it continues with intemitent problems.

Sometimes it will not operate the central locking from driver's door, but only from front passenger side, another time, not from either door, or rear trunk key.

There are 3 cables sets leading to unit...one has 3 wires, another has 2 and the other has one that plugs into a harness that has the same connector as the 3 cable one. (It has a single white wire pluging into something that has 3 cables)

What and where do I measure?

Loose Connection in door lock
 

Thanks to all the various posts, I have finally found the problem...the connector on the driver's side door lock was not seated correctly, so it would make and break contact simulating a key in the lock activating the pump!

This has been going on for years and many $'s later, it was a simple connector that just needed to be reseated.

I used this link to get the door panel off:

http://12.96.14.5/~engatwork/CkStrap.htm

The amazing thing was it only took about half hour...I have to wonder if the folks who replaced the pump (twice) will give my money back!