I replaced my door locking mechanism on driver's door last year.
The symptom was unreliable locking.
Now the same symtoms are back, but the locking mechanism was completely changed.

Is there a know second source for these kind of issues ? (cables ? control units ?)

 

Was the replacement actuator used or new?
I am assuming that you lock all doors with the remote and
the driver's door does not lock?
Will it then lock with the key?
The driver's door lock is unique and not only
uses the usual micro switch but also has two wipe type
contacts which I believe are status switches.
All these switches can wear and fail.
I know that a micro switch can become unreliable before it fails.
If your replacement actuator was new these problems should not apply.

I suppose there is a possibility of bad connection somewhere.
The other possibility is that the cable between the handle and actuator is too tight.
Did you fit the actuator yourself?

 

Possibly a different door actuator going bad since you replaced the drivers door actuator?
One good trick is to sit in the car and watch the inside lock levers when you hit the lock and unlock buttons. Look for any that don't move or don't move very well.
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The replacement actuator was used. It worked quite well for some months after replacement.

The door does lock with the key, but the fob doesn't seem to lock/unlock. I just hear the locking of the other doors.

I fitted the actuator myself, but I didn't notice any tough cabling.

My XJ wasn't moved during winter time, and its battery went down.
But I don't think, this should affect door locking ?

 

No the flat battery will not affect the door locks after charging.

If the door always locks with the key then the micro switch is ok.

I think it's a worn status switch in the actuator which

would be very difficult to repair since you have to destroy the actuator to get at them

New driver's actuator will be $400

It's not the DDM because the other doors work

As a matter of fact I have the same problem on my Jag and it has improved

Now it only occasionally will not unlock but always locks along with the other doors

I suggest that you live with it for quite a long time and see what happens

 

When swapping the actuator, I opened the first one.
There was a micro switch visible, with some welded contacts.

Is there a second switch inside the actuator ?

 

Yes buried inside two contacts
See the Electrical guide status switches

 

Is the problem all about locking as you write or also about unreliable unlocking?

If it’s unlocking ok but there is only a problem with locking there may be an issue with the sensors that detect closed boot lid or closed engine compartment. If either of these doesn’t report to be closed the key fob doesn’t lock, but will still unlock. Also the button in the dashboard and the key in the driver’s door would still lock then, but not the key fob ( that’s the situation in my car at least after the boot-lid lock got a problem )

 

Its about locking and unlocking.
The other doors lock/unlock, but the driver door doesn't. With my replaced actuator sometimes did lock/unlock, but my replaced one now seems to refuse work in either case, all the time.
I'll try the knob on the dashboard, as I only tried fob and key.
The other sensors seem ok to me, as I don't get the accustic signal of an unlocked door.

 

I opened my actuator, which came with the car. The microswitch close to the white wheel is already removed.
As I learned, that there is a second switch, I'll try to swap it, too.
But how to get there ?
( I found two small clips on the side and one big clip, but the case is unwilling to open.)