I have a 97 e36 coupe and I had an aftermarket alarm fitted around 18 months ago (Cobra if it matters). The alarm is connected to the central locking so the doors lock and the windows close etc.

Tonight I went out and the car opened fine but when I tried to lock it the alarm activated but the doors didn't lock. When I put the key in the lock the drivers door locked but nothing else. The passenger door lock only turned a little way - it won't open but the knob didn't go right down.

Anyone know what causes this and how to fix it? The cars advertised for sale right now too so I'd like to get it done quickly because that wouldn't look too good if someone came to see it. Thanks.

Do the doors lock correctly when you press the OE central locking button on the center console?

I don't have one of those.

UPDATE: I've been thinking about this all day. I just gave the passenger door a good squirt of WD-40 and turned the lock a few times and it has freed it up now. It feels like the solenoid is being pushed but it's not doing anything. I'm about to take the glovebox and stuff out to have a look at the control unit.

Out of interest the auto window closing mechanism still works although the doors don't lock - don't know if that might be a clue to someone as to where the problem is.

FINAL UPDATE: I've spent most of this evening poring over wiring diagrams and taking the dash of my car apart.

The problem is fixed but not from all that work! The windows still working thing did it for me. I (after an hour of other stuff) had a look at the fuse box and there are 3 separate fuses for the central locking system. One was quite obviously blown and as soon as I'd changed it it all worked fine.

Then it took me 30 mins to put everything back together.

The passenger door lock not turning seemed to be unrelated - just coincidence when I needed to use the key. It is working fine now since I sprayed it.

There is a known problem regarding the wiring harness that leads from the body to the trunk lid. My recent central locking failure was a direct result of frayed wires in that harness. Fuse No. 35 kept blowing as soon as I tried to use the car's central locking system.

There is a discussion thread at the top of the E36 forum regarding this problem. If you continue to have problems with your central locking system, you should check it out.