jmr1, please take the time to fill out your profile with location, model, body style, etc. We can assist you better if we know this pertinent info, You might have MB tech or more knowledgeable forum memeber living nearby. As far as your locking system goes, has your car been butchered with an aftermarket remote? If so, this could be the cause, but probably not. I had an incident with my 1994 E320 Wagon when I came out the garage to get Lotto tickets out of it and the doors were locked with the key in the ignition. I got the extra key and as quick as I could manually unlock, it would lock. I had to pull the handle real quick upon unlocking to get in. I meticulously removed the after marker alarm/remote. and still had the problem. The Vaccum/ Pressure pump operates in a twofold fashion. When you unlock, the pump rotates to create air pressure, plungers go up/ door open. When you lock, the pump rotates to create vacuum, plungers go down. The pump is under the right side rear seat. The wagon is tough to access, the way I like to have access. I removed the whole rear seat so I could fold the carpet forward. What is your locking system doing?? You'll have to go through a process of elimination. Basics first: Check all fuses, try to activate the lock system from each lock. I bought a new pump from the dealer which was about $200.00 and problem was solved. I was an MB/ Porsche tech for many years along time ago. So naturally I took the pump apart 3 or 4 times and attempted to troubleshoot the voltage signals to the pump to to isolate the problem thinking it could be a signal from the driver's door, passenger door or rear door. If you determine it's the pump, don't waste your time messing with it. Just get a new pump. I'll attempt to attach a PDF file on the lock system. I saved this recently from another posting, I can't remember the OP, but many thanks to you......................Thor
When you insert and twist a key in the front door or trunk lock cylinder you move a rod to manually unlock that door and also move a vacuum chamber diaphragm that is part of an assembly that includes an electric switch.
The switch signals the vacuum pump (under the rear seat, passenger side, in a foam box) to run and evacuate the tubing going to all the vacuum servos in the car. They are in each of the doors, near the trunk lid pushbutton, and by the fuel filler door. Only the servos in the front doors and by the trunk lid have electric switches. The others are dumb.
The pump runs until the tubing is sufficiently evacuated to move all the vacuum servos and also a diaphragm inside the vacuum pump. Then the pumps turns off (since it believes that all doors are unlocked). If the vacuum system has a large leak the pump circuitry includes a built-in timer which shuts off the pump in 30 seconds or so. This is to prevent the pump from running until it burns up or depletes the battery.
If your central locking system doesn't work at all you should check fuse C in the underhood fuse box to verify that it hasn't blown. If the power antenna works Fuse C is okay. Then go to the vacuum pump and see if you have power on the red wire plugged onto the pump (2 pin flat connector).
After that it gets more complicated. You have to check the signals to the pump at the round connector (3 pin).
Thanks for the info on the locking system, sorry about the delay getting back with you. The car is going in for other stuff, left control arm and strut, and I'll go over the problem with the shop then. I see what your talking about with removing the seats in order to get to the part, but with my back (not good) it would be a challange at this time. Lets see what they have to say about issue/cost and trying to stay within my budget.
The right side was done last week.
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