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

Forget using 850 parts, total redesign.

Because the motor is running, trying to lock the door, I suspect that the shaft between the motor and door lock is no longer connected - stupid plastic parts!

You need to remove the door panel to find the problem.
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Keeping it running is better than buying new

Klaus-
Thank you for your advice. I read about a failing door plastic part on another board. This could be the problem...
http://volvospeed.com/volvo_repairs_how_tos/doors_latches/x70_latch_repair.html
I will investigate
Wally

That is for an older model, it doesn't apply to your car. You might want to look at this one:

http://forums.swedespeed.com/showthread.php?178404-Replacing-the-door-lock-actuator
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Keeping it running is better than buying new

I am happy to report this problem has been solved. I purchased a used door lock actuator at a PNP and installed it (well, actually had to purchase two actuators since the first one was broken). There does not seem to be any easy way to open up the actuators and repair them.