Central lock system problem. Running out of idea

[R100RSCA]

Hi Everyone,

Need help again on my 1994 S350 diesel again. The driver door will not lock or unlock with the remote, but all other three doors and truck lid lock work just fine. The switch that locks/unlocks door on the dash board doesn't work at all.

Since other door locks are working, I assume the pump should be fine. The switch that locks/unlocks door, could be just switch itself. So I leave that one alone for now.

At the beginning, I thought the problem would be either the actuator, or the tube connects to actuator leaks, or no power feeds to actuator. So I bought a new actuator, disconnected power connector and air tube from old actuator, connected them to new one. I was hoping it will solve the problem, but it didn't! When I use the remote to lock/unlock the door, I can see the new actuator is trying to move, but it barely moves, probably expands/retracts about 1/16 inch and that's it. I disconnected the air tube from the actuator, try to lock/unlock the door, I can hear the air hissing. So what could be the problem? I also switched the driver door, driver side rear door air tube on the pump end, rear door always works, so the pump is definitely OK. Am I getting a defect new actuator? The power feeds to the actuator is not up to standard (volts/amps)? Or the tube leaks so there is no enough force to expand/retracts the actuator? Does it have anything to do with the switch I mention above?

Any help is greatly appreciated! I am really out of idea at this moment, what should I try next? But a new tube, connect the actuator to the pump to eliminate the possibility of leak? Anything else?

[barry12345]

I do not know the strength of the actuator. Is there a chance the actual lock /release mechanisim is too bound up somehow for it to handle?

Physical comparison with another actuator in the car as to activation strength might answer some questions. I suspect all activators are fed from a common source.

[R100RSCA]

Forgot to mention that I just connected the power and the air tube to the new actuator. I didn't connect any rod to the new actuator at all. It is just hanging there. So there is no resistance from the rod whatsoever. That's why I cannot eliminate the possibility of a defect actuator even it is new.

Thank you for the reply.

Originally Posted by barry12345

I do not know the strength of the actuator. Is there a chance the actual lock /release mechanisim is too bound up somehow for it to handle?

Physical comparison with another actuator in the car as to activation strength might answer some questions. I suspect all activators are fed from a common source.

[R100RSCA]

All doors use the same pump, but each door has its own air feed.

Originally Posted by barry12345

I do not know the strength of the actuator. Is there a chance the actual lock /release mechanisim is too bound up somehow for it to handle?

Physical comparison with another actuator in the car as to activation strength might answer some questions. I suspect all activators are fed from a common source.

[Jeremy5848]

You are on the right track. You should be able to test the new actuator by connecting it to the vacuum line for one of the other doors. Unlikely that the new actuator is bad (but not impossible). Given the route that the plastic hose has to travel to get from the pump (where is it in an S-class?) and through the accordion rubber into the door, I suspect a leaking or kinked hose, possibly in or near the door-to-A pillar accordion rubber, or a binding lock as Barry wrote. Test that by pulling/pushing the inside door lock knob or by turning the key from the outside. Compare to the passenger door.

Jeremy

[R100RSCA]

Guess I have to remove the passenger side front door panel to test the new actuator. If it works, then must the air tube. I would be very upset if it is a defect new actuator. By the way, why the actuator needs power connections? What's that for?

Originally Posted by Jeremy5848

You are on the right track. You should be able to test the new actuator by connecting it to the vacuum line for one of the other doors. Unlikely that the new actuator is bad (but not impossible). Given the route that the plastic hose has to travel to get from the pump (where is it in an S-class?) and through the accordion rubber into the door, I suspect a leaking or kinked hose, possibly in or near the door-to-A pillar accordion rubber, or a binding lock as Barry wrote. Test that by pulling/pushing the inside door lock knob or by turning the key from the outside. Compare to the passenger door.

Jeremy

[Jeremy5848]

Originally Posted by R100RSCA

By the way, why the actuator needs power connections? What's that for?

The electrical plug is not a "power" connection: it is a "signal" connection—it tells the other locks to "lock" or "unlock."

[R100RSCA]

That makes sense. I saw the actuator tried to move to different directions. More than likely it is the defect actuator or leaking tube. I will bet on tube. Thank you.

Originally Posted by Jeremy5848

The electrical plug is not a "power" connection: it is a "signal" connection—it tells the other locks to "lock" or "unlock."

[babymog]

Pump for the locks and seats is under the rear seat, curbside, for the doors is in the trunk.

[sixto]

Sounds familiar. This might help - 95 S420 front door panel removal

Sixto
83 300SD

[R100RSCA]

I haven't gone that far. I didn't connect the rod to the new actuator. Still it wouldn't expand or retract much.

Originally Posted by sixto

Sounds familiar. This might help - 95 S420 front door panel removal

Sixto
83 300SD