I am trying to troubleshoot the rear passenger door power lock. Door opens from inside and outside but lock on door must be manually operated. Power lock doesn't move door lock but works on other doors and makes an audible buzzing sound on non-working door.

I was considering trying to replace the defective part at junkyard but am not sure if it is the actuator or something else. Any thoughts?

I wonder if earlier volvos (850? ) might have compatible parts? Thanks

Wally