Central Locking Problem

[MBEN]

I have a 2001 130 TDI estate which has developed a problem with the central locking. It unlocks fine (every time) using the fob but will only lock intermittently via the fob, every thing works well using the key in the lock.
I have tried the spare key with the same results so rule this out, which to my mind leaves the central locking unit in the door or the CCM in the passengers footwell, I suspect the former but would appreciate thoughts before start taking things apart.

Thanks, MBEN

[martin1810]

If only one door is involved it is more likely to be the door control unit or wiring from the ccm to the door control unit. This doesn't mean it is not the ccm playing up though. A fault code read will sometimes help by telling you that the ccm can't communicate with the door control module. That then suggests a wire or door module problem.