Rear door won't lock or unlock automatically
 

Hi guys,

I've got a car which the passenger rear door won't lock or unlock automatically, no matter by key fob, door switch on driver front door, or even key turning. I can lock and unlock the door manually from the internal. The other three door work well. And whenever I tried to activate the automatic door locking/unlocking, I can't hear the locking/unlocking sound from that P rear door which I can always hear from the other three doors. Do you think it's the problem of door latch assembly or actuator? Or from anything else? Thank you very much!