Hello,
The central locking on my wifes Focus 1.8 Ghia 02 plate has a fault.
When I try to use the fob it locks then immediately unlocks, the only way the lock the car is to go round to the passenger side and lock it by putting the key in then turn, then you can press the the fob and double lock the car. You cannot do this from the drivers side for some reason.
Any help would be greatly appreciated.
Many thanks, 
Hi...
The reason the car immediately unlocks after locking is because the central locking control unit is being told that one of the doors or hatch door or bonnet is open,this can be caused by one of the door close switches not working.
It can also be which is more likely that one of the doors has a locking fault and is not locking on remote locking and the car immediately unlocks to warn you that the system has not fully locked the car before you walk away from the car.
As you can lock the passenger door with the key then the locking works ok then I would try the following -
Use the central locking on the key to lock the car making sure that all doors etc are well shut,
as you do this look through the drivers door window to see the passenger door interior lever,this should move inwards as you use the remote locking button.You can also check this on all the 4 main doors.
If the passenger door lever does not move inwards then the fault lies in the door,a locking motor fault or loose connection or stuck lever fitting.
I thick what is happening is that when you put the key in to the passenger door you are locking the door by manual locking then the control unit will shut all the car by double locking and then the unit understands that all doors ect are locked ok and will not immediately unlock anymore.
We have had such bad damp wet weather that dampness in the doors and connectors are a problem
and wd 40 sprayed on door connecting fittings and locks are a must to keep good operation.
Bet the fault is in the passenger door.
Hope this helps good luck.