EDS300-400

The central locking on my W124 300E (1988) stopped working suddenly yesterday. Unlocking driver's door does not unlock other doors (or trunk). Everything needs to be unlocked and locked manually, including the trunk. If I manually lock the passenger side doors with the driver's door still unlocked, and then open the driver's door, it sets off the alarm, which I can then shut off by turning the key in the driver's door lock counter-clockwise to unlock (even though it is already unlocked). Locking it does not turn off the alarm. It has always worked fine since I've owned it (about two years) though the pneumatic lock has always seemed sluggish to me, though I have nothing to compare it to other than modern cars, all of which lock almost instantaneously. It is not a fuse problem. I haven't found anything on the threads that addresses this directly. I am not particularly knowledgeable about mechanics or electrics, but do love these cars. Does anyone have any suggestions?

khomer2

Before going through the vacuum lines, check your fuses first. Replace or clean the fuse for your central locking system.

EDS300-400

I did check the fuse and switched it for a good one just in case. it's not the fuse.

khomer2

Does your w124 have the Anti theft alarm ATA module? I believe that also controls the central locking system.
You can dig further by looking into the wiring diagrams ====>
https://freescruz.com/.priv/W124/Ind...rbleShting.htm

EDS300-400

Thanks, Khomer2. I haven't the slightest idea whether my W124 has the anti-theft module you refer to, and unfortunately the wiring diagrams might as well be in Chinese to me. Is it possible it's the anti-theft system that is the problem? Though I would note that anti-theft seems to work. Today I got out of the car, locked the driver's side door and then realized the RR door was unlocked. When I went around and opened it in order to push the button down manually, the alarm went off.

khomer2

You have the ATA if the alarm when off - btw, the Alarm module is located on/under the floor board, passenger side. Pull the heavy carpet up and backwards. There is a screw securing the cover plate you will see.

Vacuum check-
You can start checking the central locking vacuum connections too. You may have a leak somewhere.

EDS300-400

Thanks again Khomer2. It sounds like a vacuum leak to me. I will check it out and report back.

khomer2

My simple vacuum test on these older great MBs is:
When I turn the DS door key CW, I watch for the timing of the door plungers to see how long they take to lock (go down) relative to the DS plunger.
If it's not instant (within 1-2 secs), then there's a good possibility there is a (small) leak somewhere.
Ah.... we all get leaky as we age into the Sr, years....

EDS300-400

That is precisely my non-technical and inexperienced test as well. and my plungers have been relatively slow, I think, though, again, I am not sure what to compare them to. One or two seconds is actually rather long, no? I mean, it definitely seemed to take them a full 1-2 seconds to go down, and even then, they seemed like they were working hard just to do it, (kinda like us as we age .... )

khomer2

Another note/ checklist I have on the w124s:
Can you hear the vacuum pump whirring?
When you activate the door locks for both lock and unlock, if you hear it whirring, then typically, there is nothing wrong with the door switches for the power lock system.
But, If the pump whirrs for say, 5 seconds or longer, then you have a leak, either in one (or more) of the lines, the door actuators, or inside the pump itself.