Taxi Driver Online

so my tx4 rear passenger door wouldn't lock from central locking. all other doors did.
i replaced the actuator but still didn't lock.
now for the strange thing, i lock the cab (faulty door not locked) then lift the locked front door handle next to it and hey presto!! the rear door is locked?
there's no sound of it locking when i lift the front handle with my ear to the faulty rear one.

Every time? What happens when you then try to unlock?

I'd expect the actuator to make some noise.