Car is a 97 EL Fairmont Ghia 5.0, and it has a central locking issue.

When using the remote the doors have stopped locking. Instead the button goes down momentarily and all the doors 'lock' and then they all open again and the button goes up. The horn sounds about 5 times very quickly and the indicators flash. This is exactly what the car would do normally if one of the doors was open when you tried to lock it. Yet if you lock it with the key in the door lock, all the doors lock fine, and unlock fine when you use the key to unlock the car too.
(If you use the remote to unlock the car, its alarm will go off when you open the door as Im guessing using the key to lock the door doesnt arm the alarm, and when you use the remote to unlock it, it does arm the alarm, hence you have to press the remote button twice to stop the alarm going off.)

At first a search indicates a faulty door lock module/motor. But the car is NOT cycling through the lock-unlock-lock-unlock phase that this problem seems to cause. It is only locking then unlocking the once, exactly as it would if a door was left open.

Next I checked all the door closed push buttons (incase they had any effect on the central locking, not just interior lighting) these all appear to be working fine.

Any ideas on what my problem could be?

Hi, thanks for the reply yes I opened and closed every door. Each turns on the light and turns it off. Turning off takes about 20-30sec (due to the fairmonts 'fade out' I think), they go on and off instantly if the ignition is on too.

To be honest I have never owned a car with an alarm before, what is valet mode and how would you do that?

And nope havn't done any electrical work other than getting a map reading globe in the main interior light to work correctly (one of the contacts was slightly bent), around the same time the problem started to occur.

Just found some receipts. Appears to be a "Code" brand alarm, purchased in 2003.

It just uses the standard falcon remotes to arm and disarm it as far as I can tell.

Just another point, if you press the central locking button on the dash, it will lock and unlock the doors same as it will when you try to use the remote, but it doesnt beep the horn really fast and flash the indicators, just does the lock-unlock part.

Cheers