94 S350 (140)
My driver's side door lock will not open everytime when I use the sending unit or use the key from another position. Nothing found in my search. Any one have this problem before me? How was it fixed? All other doors, trunk and the fuel door work fine.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

This is strange, if you use the key it should pull the diaphram which contains a switch in the drivers door to start the motor and unlock all the doors thru the PSE. The remote should send a signal thru the sensors in the door handles and also start the PSE. By the way the PSE is the locking, rod, headrest, lumbar,HVAC support, pump under the rear seat. I hope this gives you an insigth in the way it works.

I was speaking with George Murphy about my door lock problems, and he was kind enough to send me the following:

140 door lock problems

Recent experience with the vacuum pumps that provide door locking on 140 S-class cars has shown that in older cars, say 1995 to 1992- the lubricant on the door lock mechanism seems to be degrading after 10 year or so, causing more resistance for the vacuum actuator that operates the lock. If the computer detects two failures to lock, the computer "locks out" the vacuum pump, preventing future operation. If you pull and re-install the fuse for the pump, it works OK again for a few cycles, then locks out again.

A new (expensive) pump works OK for awhile, then locks out as before.

The solution is to dismantle the doors and clean and re-lubricate the mechanical parts of the lock mechanism operated by the vacuum actuator.

I have only tried this on one 12-year-old 140 class, but it did resolve the lockout problem with the original pump. You should also check that the pump delivers at least 2.2 bar pressure.


Regards,

George Murphy
MBCA Technical Director

865-482-9175 9am to 5pm ET M-F

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

i think that you need a new vacuum lock device on the drivers door.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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