How can i fix the central locking ?

Drivers door lock position sensor is probably faulty, this tells the locking system to lock or unlock all doors. The vans have the rear doors open on a separate button on the fob as I remember, the locking acts on all, that is unless the system thinks the front door is locked ! Remove the trim panel and look around the lock barrel you will see a a plastic ring a bit like a big polo. This is the position switch, it can be removed by splitting the circular section into 2 halves by releasing a plastic clip. The switch can then be removed for inspection/replacement.

Good luck SB

Steve
November 2006