I have a strange problem on my 1990 xj40. The central locking will engage from the key, door button, or dash switch but will not unlock with the key.
The fuel flap also will not open (I only mention this here, in case its connected)

The previous owner has somehow disabled the lock on the N/S/R door, so the rest can be locked leaving that door for access.

I have twice tried the reset method suggested on this forum (disconect battery lock and unlock doors a few times, lock doors and reconnected battery) but no joy.

any other suggestions appreciated, as I cant bring it home until I can lock and unlock it.

 

Think I may have solved two of the problems today. Just bought front door handles and key off ebay, as I suspect I dont have a door key.
and the fuel filler flap - I forced it open and have turned the rod through about 30 degrees, so I just have to press on one side of the flap and it opens.

 

I get a similar problem if someone tries to open the passenger front door while I am unlocking the drivers door. It seems to upset the central locking control unit. The solution I found was to lock all doors then try to open the drivers door although I have found it takes a few attempts.

 

I solved it by buying new front door handles and key. It seems I didnt have a door key, at all. The rear ones are now playing up, i suspect wiring or switch.