locks keep unlocking

[mjhmjh2]

on a 1988 W124 250TD with vacuum operated locks, I lock the drivers door (the only one that actuates the central locking) and 20 seconds later it unlocks itself...

Any ideas?

Matthew

 

[television]

I would think that the fault is in the lock as the pump can only run for 20 sec

http://www.detali.ru/cat/oem_mb2.as...GM=717.417&CT=F&cat=45P&SID=80&SGR=045&SGN=03

 

[mjhmjh2]

any idea how the system works or reads the lock position? I'm guessing its something to do with that.. I cant really follow the diagram - it doesnt help that half the things are labelled up as no 005 although I'm guessing thats vacuum pipes.

 

[mjhmjh2]

just done a bit more testing. If I started the car and tried the lock, it would lock and stay locked. If i stopped the car (but left the key in the off ignition point) it stayed locked. If I took the key our of the iginition it would not stay locked.

The pumps/mechanicsm operates for about 5 seconds then at the same time each time (aroudn 14 seconds), it unlocks.

So what does taking the key out of the ignition do (after turning to one of the ignition positions)? I know it lets the headlight warning buzzer work.

Could it be something as 'simple' as an earth fault somewhere?

Is the vacuum actuation dependant on an electrical sensor?

Thanks
Matthew

 

[television]

just done a bit more testing. If I started the car and tried the lock, it would lock and stay locked. If i stopped the car (but left the key in the off ignition point) it stayed locked. If I took the key our of the iginition it would not stay locked.

The pumps/mechanicsm operates for about 5 seconds then at the same time each time (aroudn 14 seconds), it unlocks.

So what does taking the key out of the ignition do (after turning to one of the ignition positions)? I know it lets the headlight warning buzzer work.

Could it be something as 'simple' as an earth fault somewhere?

Is the vacuum actuation dependant on an electrical sensor?

Thanks
Matthew

Ouch, do you mind if I chew this over and come back to it, thanks for the good dianosis

 

[mjhmjh2]

please do chew it over - any ideas would be gratefully received... I'm guessing its got to be electrical (otherwise it would not have any connection with ignition position)... So the most likely thing is whatever sensor is near the door lock mech I'd reckon (if there is indeed such a thing).. I'm hoping that it doesn't see the change in pressure from the drivers lock actuator, cus that means there is some vacuum sensor somewehre

Matthew

 

[television]

no this will not be a vacuum fault

 

[anyweb]

if you set your heater controls to UP (ie heat full and blowing to windscreen but with no power) confusing i know, then do you still have the same problem ?

i'm curious as i had a weeeeeeeeeeeeeeeeird issue with vacuums before on my old 190d and the heater controls (whether the heater was on or off) positions changed the nature of my vacuum problem

hence why i mentioned it, could be a total red-herring but still, ya never know

my issue was more severe than yours though, if my heater dials were pointing anywhere other than mentioned above, then the car wouldnt turn off even after i had pulled out the key

hilarious really but really disturbing the first time I noticed it.

cheers
anyweb

 

[mjhmjh2]

locks keep unlocking - FIXED

Ok so I spent a couple of hours playing this afternoon. With a bit of hindsight the job would have been a bit easier than I made it, but as I had none, I decided to proceed as follows:

I removed the drivers door card, expecting that to be the culprit of the problems. Since I've had the car it has only unlocked by the drivers door. As I mentioned this earlier and no one corrected me I assumed this was by design. So if that was the only place that actuated the vacuum mechanism the problem was most likely there.

Following the haines manual was pretty straight forward until the move forward and lift away - it didn't.. It quite clearly lifted upwards, but I only realised that after I'd broken the pull handle mechanism mount points. So another 30 minutes wasted drilling and tapping the remains of the plastic handle to door card mount points. It was shame to use best stainless machine screws and washers, but hey ho!

Pulled off the electric connector from the lock and simulated the action of the lock with a piece of wire. Still the same symptoms sometimes intermitantly.

I'd studied the wiring diagram so I knew that the passenger door and tailgate should have actuated the locks as well. It was a50/50 decision as to tailgate or passenger door (I was erring on the side of the passenger door). However I'm glad I picked option 3 and that was to locate the vacuum pump.

At the vacuum pump I found a perm live and perm ground on one connector and 3 wires, one going to each door actuator. The way the system works is that each door sends either a live or ground on it's respected pin. Live for lock open, ground for locked closed. I found I could activate the pump and lock the doors by putting a live signal to the drivers door pin and unlock by switching it to ground. I measured the signal on each of the other wires with the lock mech in both positions. (whilst all the locks actuate ok) the tailgate signal stayed in unlocked, the passenger side in locked.

Now what I suspect was happening was drivers door was telling the mech "I'm locking", when the pump stopped the signal from the boot was "I'm unlocking", hence the pump woudl then unlock. This was slightly intermittant but in the last 2 days has been pretty reproduceable. What I cannot figure out is how the ignition lock could interact, the only thing I can think of is there is enough stuff left switched on to drop the voltage far enough for the tailgate not to pass enough voltage to the system.

Anyway the tailgate electrical mech is now disconnected - as I don't have a key for the tailgate anyway there is little point in it being connected.

Hope some of this will prove useful to someone in the future. Now on to the next problem!

Matthew

 

[television]

Mathew, you are very kind with your post, and thanks, maybe we can help you in return one day

 

[mjhmjh2]

Mathew, you are very kind with your post, and thanks, maybe we can help you in return one day

there was me thinking it was a useless rant! So thanks!!!
Matthew

 

[television]

there was me thinking it was a useless rant! So thanks!!!
Matthew

Never in a million years, these are forums where all aspects are discussed, sometime we can be stuck in what direction to go on a hard fault. OK we get all types of answers, and it can be the strangest of answers that can lead to solving the fault just by throwing up ideas.