Central Locking Has Mind Of It's Own, Appears to have grown brain

[Ciaran]

Hi folks,

i was wondering if anyone has ever encountered this one. Recently, in the past week or so, the central locking has begun locking itself almost continiously. I have to be really careful not to leave the keys in the car, as as soon as I get in or out, the doors lock almost instantly. It will lock at other random times too. When starting the engine, when just sitting idling at lights, when driving over bumps, or even when the car is just sitting turned off, shortly after everyone has got out etc. It's totally random so I don't know if its mechanical or electrical.

One thing to note though, is that when it does lock, the dot matrix goes to permanently saying 'Right front door open', so I'm guessing that the driver's door is causing the problem somehow.
I'm guessing theres some kind of sensor in the lock mechanism inside the door that tells the dot matrix when the door is supposedly open? I don't suppose anyone knows if the central locking happens to get it's information from the same sensor / switch?
I've also noticed in the past day or two that I can no longer lock or unlock the central locking using the pin on the drivers door, though opening it with the handle, or using the remote works fine. It never spontaneously unlocks, thankfully, just locks.
I'd appreciate any thoughts, and specifically if anyone has encountered this, or stripped down the lock mechanism. It's going to be a fun weekend I suspect

Cheers.

Ciarán.

[noz]

Hi Ciaran,

First of all a quick description of the operation of the locking system:
(sorry if this sounds pedantic but understanding the mechanism will lead to understanding the solution)
All the door lock motors operate simultaneously and the same motor runs forward and reverse for lock and unlock respectively. When the system is at rest ie when not in the process of locking or unlocking there is no power to the locking motors.
Upon receiving the signal to open or close the Central Locking controller (ecu) sends a voltage of the correct polarity to all the door lock motors. The power stays on to the motors until the end switches in the each of the locks signal back to the controller that the lock has reached the end of its travel. This signal must come back from all doors, not just the drivers door. The same thing happens when the ecu receives a signal to perform the reverse operation. There are end switches to sense the locked and unlocked status of each door switch.
There are two devices which send the open or closed signal to the Central Locking ecu. One is the Plip receiver and one is the door lock itself. The signals from both of these devices is 'momentary' rather than continuous (latching). ie the switches involved are spring return and are not held in constantly. The plip receiver simply energises one of two wires connecting to the central locking controller to open and close respectively.
The front doors are slightly different. The button on the inside of the door, the internal door handle and the external key all act together on the one set of contacts. The contacts are located in the complex array of components mounted inside the door which constitute the 'door locking mechanism'. It looks like something out of a mad frankenstein movie. All of the three mechanisms are connected to the DLM by a series of levers rods and pivots. Any one of the three mechanisms can activate the microswitches. When any of the three mechanisms momentarily touch a particular microswitch this initiates the command for the ecu to open or close the locks. Once initiated the said mechanism is released.

OK, thats how it should work.

Now consider what happens when the mechanisms sieze up and become stiff to operate. If the lever which finally presses on the 'open command' microswitch siezes or sticks then this microswitch will remain in the 'made' position permanently. When one of the three mechanisms above is activated to, say, close the locks then the locks close. However, because the 'open command' microswitch is permanently 'made' then the controller immediately gets the command to open again. This results in the inability to lock the car. Every time it locks it immediately unlocks again ! Now picture the same situation in reverse. The car would remain permanently locked. However, the close signal is prevented from being activated when either the door is ajar or the ignition is on. So the car appears to lock itself when the ignition is off and you've stepped out of the car and closed the door. Intermittent occurencies of the symptoms simply means that the mechanism is stiff just at the point of contact of the microswitch and the slightest vibration sets it off.

Solution
Take the inner door lining off. Press on the 'sneck' at the edge of the door with a false striker to fool the locking mechanism into thinking the door is closed. Operate the door locks with the plip or key several hundred times whilst lubricating the whole of the locking mechanism with your favourite release fluid. If that doesn't work then the locking mechanism has to come out for repair. This is not an easy task particularly because the window guide is in the way. However, it can be achieved but a lot of patience is required. Lets hope squirting with release oil does the trick.

Hope that helps. Please let us know how you get on.

Cheers

noz

[Peter.N.]

That's a very good explanation Noz, even I can understand it!

Peter.N.

[Ciaran]

Hi Noz,

Many thanks for that comprehensive and in depth explanation, must have taken you quite a while typing all that in!
I have done some work on the central locking before in my other cars, so am aware of the concept of how they work... however this being an XM, I thought I'd better check, in case there was some nuclear powered lock motor with strawberry flavoured linkages or something Thank you for putting my fears to rest.

The thing that makes me suspect the driver's door as being the source of the lock signal, is the fact that the dot matrix displays 'Right front door open' everytime the doors lock... that and the fact that the internal lock button on it no longer does anything, but the handle and plip unlock / lock it fine.

I'll try and get the door cards off today and lubricate everything, if I get a chance... unfortunatly the starter motor problem has returned last night / this morning, so I fear I may spend the day chasing that instead. Well, at least the chances of someone stealing it are low... what, with intelligent self locking doors, and a starter that doesn't.

Many thanks for your help!

Ciarán.

This post has been edited by Ciaran on December 09, 2006 12:08 pm

[Ciaran]

Hi folks,

Well, I did get the door card off the driver's side briefly. It's definately the door causing the issue, as there was a particular multiplug on the bottom of the lock mechanism, and when I wiggled it the car locked and unlocked like mad at the slightest touch.
I found three multiplugs in total, the aforementioned brown one at the rear, which was 4 pins I think, then one in front of it, a white one with 3 pins, then lastly a 2 pin one above them, which I couldn't unplug because it was fouling the side impact bar. Does anyone happen to know which of these plugs is responsible for what exactly?

I cleaned the plugs out with electrical contact cleaner as best I could, but access was very limited. I couldn't really get lubricating any of the linkage bars, as I couldn't even see them. I did try unbolting the lock mechanism from the edge of the door and seeing if I could shift it forward slightly, but it was hardly budging.
However, I did work all the rods several times, and now the door locks / unlocks with the internal button. The jury is still out on whether this has fixed anything, but (touch wood), it hasn't spontaneously locked since then... fingers crossed . The dot matrix is now behaving as well. Will report back on any further developments!

As a side note, while inside the door, I discovered this strange red 2 pin connector connected to the wiring, which doesn't appear to plug in to anything. Does anyone know what this is for? :





This post has been edited by Ciaran on December 10, 2006 12:56 am

[xmexclusive]

Hi Ciaran

The two sockets nearest the back edge of the door are the standard door lock connections. Present on both Mk1 and Mk2 XM's. The third socket , the one nearest your access hole, is the deadlock contacts and only present on a Mk2 XM.
I have a set of Mk2 doors ready to strip so I will have a look to see if your red connector is present and what it is connected to.

Regards

XMexc

[Ciaran]

Hi XMexc,

That makes sense with the two bottom plugs. The higher up one only has two wires however, is this the deadlock connection? It seems odd it having so few wires, but I guess all it needs is a positive/negative pulse...

Thanks for the offer to look at those doors. The red connector isn't causing a problem as such, just I'm curious as to what it's for.

Cheers.

Ciarán.


This post has been edited by Ciaran on December 10, 2006 12:42 am

[Ciaran]

Well, that was short lived. I just got back from picking my brother up from work.
It seems that all the doors attempt to lock, then unlock whenever the driver's door is opened. However at least it *seems* to have stopped spontaneously locking at the slightest movement / vibration.
I noticed when getting out that the internal handle is jamming in the opened position and not springing back without assistance, and the button appears to move down slightly when this happens. I'm guessing therefore, that I've managed to foul the linkage or something, so will have another look at it tomorrow. Hopefully that will turn out to be the issue..

Many thanks for everyone's help

[xmexclusive]

Hi Ciaran

It is the nearest of the two larger sockets/plugs that is the deadlocking. Sorry about the confusion but I just have handy a couple of removed door catches (one Mk1, one Mk2 for same door). I do not remember which door as I just put them to one side to be able to compare the differences between Mk1/Mk2 door catches.
The sockets are as follows:
Deadlock - large oblong with single row of 5 pins.
Door locks 1 - small oblong with 2 pins
Door locks 2 - large oblong (as deadlock) with single row of 4 pins and a missing pin the end nearest the 2 pin socket
The plugs and sockets have a pattern of plastic polarising lugs so that it is not possible to connect them up the wrong way round.

So there are 5 wires to the deadlock and not 2.

Regards

XMexc

[Ciaran]

Hi Xmexc,

That makes sense now, interesting that wiggling the deadlock connector seemed to trigger the symptoms with the lock.
Willie Johnston had a quick look at the door today in the pub carpark and his prognosis is that the lock itself may be faulty, one of the possibilities that Noz initially suggested. Unfortunatly the weekend is over, so it will be next week before I have another chance to have a look, but will report back any progress.

Cheers

Ciarán.

[xm_on_a_shoestring]

I had that problem on my XM2.0sei hatchback 1990 (my first xm!). I cured it with a replacement lock. The locks incidentally are different on Mk1 & 2's on the front doors.

Shoestring

[Ciaran]

To return to this briefly, I don't want to tempt fate, but the self locking issue has gone away since I changed the malfunctioning battery about a month ago...

It was a new battery back in August, with a 3 year warranty, but I started having intermittent starting problems, and other electrical gremlins... I eventually found it had split inside one of the terminals, and was spewing this crystalised acid substance into the engine bay

Since that's been replaced, the issue has went away, but I'll give it another while before I say its gone....

This post has been edited by Ciaran on January 07, 2007 01:45 am