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1998 W140 S320LWB 65k miles
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Discussion Starter #1
All of a sudden, the passenger front door locking knob stop responding to either the remote or the console lock button. It will respond to unlock sometimes but definitely not responding to locking (going down).The other doors all work normally.

However, I can still manually push it down or pull it up to lock/unlock...

How do I determine if this is a problem with lock actuator or vacuum leak in the line to the passenger front door? The pump should be OK since the other doors do work.

Thanks!
 

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DOORLOCK ACTUATOR FAIL

I have axactly the same symptoms on my '99 S420, same door, same malfunction. Vacuum connection checked OK at the pump, underneath the back seat. Doorknob is sometimes hard to push down, I will not force it. Can anyone provide door panel removal process and how to troubleshoot the actuator? Pictures of the actuator or how it supposed to "actuate"? Gtseng and I can sure use some help here, thanks.
 

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1995 Mercedes-Benz S420 (W140), 1997 BMW 740iL (E38), 2011 C300 Luxury (W204)
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1,314 Posts
Yup. Door actuator. I believe the passneger actuator does not have an electrical plug, so one less step. But the process is still a pain to work with. Carefully unplug the vacuum line to the actuator. Remove the lock links, then unscrew the actuator bolt and you should be able to just slide it out.
The door lock knob has a link that connects to another link which connects to the actuator. You have to undo the "clip" between the two links so you can unlatch the links so that the actuator can come out. I wish I had taken pictures when I did the driver door. Basically I had the same symptoms. There is a leak in the actuator itself.
 

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Thank you Sinned. Door panel removal may not be all that complicated, after all I have seen the mechanic take a panel off from a rear door once. I know I can manage this one myself. Also thanks for the process in getting the actuator un-linked and out for inspection. If the leak is within the actuator, I wonder if it is repairable as opposed to installing a new Actuator to save money . DOn't know how much a new actuator would cost. Will work on this on my next weekend off. I'll post info later.
 

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1997 S500V, 1999 S500 grand edition, 2006 s65 amg
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it literally takes about 2 minutes to remove if you know how to remove the seat control trim. there is a screw near the door latch remove that and it should come off with a black piece, next there is a screw on the hand rest part, next you take off the wood (easiest way is use an old credit card to pry it you dont have the tool there is two clips and once the clips are closed it slides off), next you will see two screws remove those and then the panel is off. next you disconnect the wires on the door you will figure it out its simple.
 
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