1995 Wagon Unlocks itself after a while?

[Dbreid]

All,
This is a frustrating one, because... well.. it is really hard to TEST.

The issue:

I have a 1995 E320 Wagon (maybe important? Tailgate?) with the Ortho seats. The ortho seats matter, because the central vac system is different. Anyway, I can lock the car normally (with the key) from the drivers door, or the passenger, or the trunk. Everything works fine, and all the locks work. Central lock works fine. However, at some point which seems like something between 15 minutes and more than 24 hours, the car unlocks itself. All the doors. They all unlock.

So I drive somewhere (or leave it in the garage) and lock it. Everything locks, seems fine, no sounds, etc. I wait for a minute or so, and nothing happens. Then I walk away, and come back some time later, and about half the time it is unlocked. I have tried to figure out pattern, but I cannot.

I figured at first it was the drivers' door lock mechanism (the vac plunger), so I bought a new OEM (mercedes part in mercedes box) plunger, and installed it. Nothing changed. Then I ordered (it was expensive) a band new Central Locking vac (under the rear passenger seat) and installed it. Fired right up, made vacuum, and everything seemed fine (no obvious leaks, etc). No change.

I have not replaced the passenger door plunger (though I have it, so I could), nor have I touched the tailgate lock.

But I am not really sure how to diagnose this silly thing. And the parts are just annoying enough to replace.... I dont own a smoke machine to test for vacuum leaks, but could probably go find one.

Any guesses on how to actually figure out the culprit?

Thanks

P.S. This is an issue other people have had: Help! W124 unlocking itself at random!!! - Page 1 - Mercedes - PistonHeads UK

But no one seem to have a good way to test it.

Thanks!!!

-Dan

 

[gsxr]

Dan, the central lock system is relatively straightforward. From memory, it looks for a wire/signal to be grounded, and locks or unlocks when this occurs. (@Jlaa ?) If so, there's a possibility of a wire in the system either randomly grounding out (chafed insulation somewhere), or perhaps moisture causing problems at a splice.

There's no remote / keyless entry or aftermarket alarm system, correct?

 

[Dbreid]

There's no remote / keyless entry or aftermarket alarm system, correct?

Not that I am aware of. I have no fob, and no weird wires and stuff.

Hmmm. Corrosion. That's easier to dig for than vacuum.

 

[Jlaa]

Dan, the central lock system is relatively straightforward. From memory, it looks for a wire/signal to be grounded, and locks or unlocks when this occurs. (@Jlaa ?) If so, there's a possibility of a wire in the system either randomly grounding out (chafed insulation somewhere), or perhaps moisture causing problems at a splice.

There's no remote / keyless entry or aftermarket alarm system, correct?

Ohhhh this is a hard one. @Dbreid, assuming you haven't done so already, I would, as @gsxr suggests, maybe start with the assumption that it might be an electrical problem and not vacuum problem? See these two diagrams ---- one for 300TE as of MY 1987, and one for all 124.0/124.1/124.2 EXCEPT 124.051 (300CE) as of MY 1990.

Note the special callouts for "Wagon only" as well as for "orthopaedic seats". Also note that there seem to be some Yellow and Red/White wires that go come from supply pump into the tailgate lock actuator. I wonder if repeated opening / closing of the tailgate has worn these wires?

I would also note that the left front door is also probably used quite frequently...... and so wires that go from those doors to the supply pump are

• Yellow, Red/White, Blue, Black - LF door

 

[gsxr]

It's definitely electrical. The control portion, signaling lock/unlock, is entirely electrical. The vacuum/pressure circuits are simply to move the physical locking mechanism.

FWIW... I vaguely recall that @Honcho had replaced the tailgate wiring harness, so that should be good wiring... but it wouldn't hurt to eyeball the routing to verify nothing has chafed.

Depending where some of the splices or connectors are located, you might try disconnecting certain parts of the system to see if the problem goes away, i.e. if the tailgate is no longer in the electrical circuit. This may be easier said than done (I've never attempted it).

 

[Dbreid]

Honestly, just looking for electrical is a helpful tip. I will try to isolate it now. Let's see.

I also wonder how the gas door lock plays in. Might be possible that is an issue, as I never really considered that before either.

 

[gsxr]

I also wonder how the gas door lock plays in. Might be possible that is an issue, as I never really considered that before either.

I can help with that question. The gas door lock has no electrical signal, only a vacuum signal. Since the entire car is unlocking, you're back to electrical. The only items which I can think of that normally trigger the electrical signal are the front door pods (which have an electrical switch), trunk/tailgate lock, and possibly a signal connected to the convenience relay - although I'm not sure if that could cause this.

 

[Dbreid]

So when you say "door pod" do you mean these things? Or something else?

 

[gsxr]

So when you say "door pod" do you mean these things? Or something else?

Yup, that's the item I was referring. It's the vacuum actuator with integrated switch, to tell the electrical controls the position of each pod (locked or unlocked).

 

[Dbreid]

OK, then now I am suspecting my passenger door. That's my next try.

 

[SVH]

Dan - I feel your pain and frustration as this same very thing happened to me last week. I too have a wagon, 94. At first, I thought I didn't lock it but after a few trips back to the car (within 1/2 hour) it was always unlocked. I thought WTF? Then, paying close attention and concerned I'd lock it as usual and a few seconds later *I see and hear* everything unlock. I was baffled! The same thing repeated after locking it. I finally discovered my rear passenger door was NOT fully closed. Your situation could be completely different. Good luck. -Steve

 

[Dbreid]

Well, I guess it is too soon to say for SURE (because intermittent things work that way), but I replaced the door vac pod/controller thing in the passenger side door, and it is fixed. However, I don't think the vac switch was the problem. Somewhere along the line the thin metal connecting rod where you screw the door lock knob (the plastic thing that goes up and down when you lock the door and you can see visibly) on to was bent. It made the plunger side a little crooked in the door panel. So I sort of suspect that the real culprit here was actually more mechanical. Meaning that when the door locked, the bent rod caused the plunger/knob to press against the door panel, and because it was at an angle, it acted to push "up" on the plunger, thus unlocking the door. I just took the rod out, and straightened it carefull in my vise and then replaced the rest of the stuff and we seem to be in business!

 

[Dbreid]

I have been testing it, and I think it really is fixed. Hope this helps someone else! Turns out it could be electrical, could be vac, but could also be mechanical.