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#1
03-17-2009, 12:59 PM
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w124 Strange central locking problem
Hello all,
My 1992 400E (205k) has recently developed an interesting problem: Using the key in the driver's side door will no longer lock or unlock any of the other doors. Using the key in the passenger door or trunk will unlock and lock everything as usual (including the drivers door). Pushing down the lock button from inside the car has the same result: The driver's side will only lock and unlock itself, while pushing down the passenger side will lock and unlock everything. I have ruled out any vacuum leaks. The pump under the rear seat operates normally and quickly. The problem is that it's not even activated in the first place by the driver's door. So, I have removed the actuator in the driver's door. The resistance values check out O.K. when I test it. Also, the electrical connector is supplying it with 12V, so I'm fairly certain this unit is alright. The switch that is attached to the door handle itself also seems to be O.K. So, is there any explanation as to what could be causing my issues? I tried jumping the switch connector to see if the doors wold lock/unlock, but all I get is a faint ticking coming from the convenience control module area. The vacuum pump does not actuate. Is there some mystery fuse, or a connection somewhere that is prone to failure? The fuse under the hood is good. Thanks for any help! 
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#2
03-17-2009, 01:13 PM
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Have you checked the wires going into the door jam between the body and door? Sometimes they can get damaged and short out....causing stuff to stop working properly.
__________________
-diesel is not just a fuel, its a way of life-  '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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#3
03-17-2009, 01:39 PM
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Vaccum element in the driver's door, its gone bad
__________________
 99 Jetta Mk3 07 Jetta Mk5 89 300E W124 10 E 350 W212 08 C300 W204 Benz's aren't mine 
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#4
03-17-2009, 02:25 PM
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On the 3 wires at the vacuum element/ switch in the door, like you saw...1 wire has power, another has ground, & the third goes to the pump.
As you lock & unlock the switch sends power OR ground as a signal to the pump.
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#5
03-17-2009, 04:20 PM
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Thanks to everyone for the helpful suggestions! I did some more testing with my multimeter and found the problem area. At the pump, I checked to see that the input wires from the driver door, passenger door, and trunk were getting 12V in the lock and unlock position. What a surprise, there was 0V from the drivers door. Upon closer inspection, I found that just a couple inches down from that connector, someone had spliced in extra wiring, I assume for an aftermarket remote locking system. I ripped out that wire and soldered it back up properly, and voila, everything works. Odd that it would randomly ground out like that, but whatever.
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