peugeot 206 [20002] central locking fault?

the fault on the central locking system is that it will not lock or unlock with the remote or key, there is a alarm fitted which works off the remote [which is working ok] i have disconnected all 3 motors [3door] and connected 1 at a time and had no joy, i have checked the wiring and all seems in order, i also locked the door while holding the lock button on the remote but this did not fix it either. can anyone help please