I just bought a 1996 Sable but didn't notice the rear left door lock didn't work when I bought it. It's a GS wagon with auto transmission, 3.0L engine and keyless remote door locks.
When I press either lock or unlock on the remote all the locks except the rear left work fine. I can't manually lock that door either. The lock arm won't move at all. I removed the interior door panel and tried to move the horizontal bar that runs between the vertical lock arm and the lock at the latch. It won't move at all. This arm runs through a plastic holder that seems to keep the cloth insulation of the arm fixed so that the arm will move inside it to lock/unlock the door.
I also tried to move the arm of the actuator but can't move it either. I held my fingers on the actuator arm and pressed the buttons on the remote. I could feel the arm move slightly but not enough to lock the door. Unlock is the same. I also pressed the lock buttons on the door with the same result and I unlocked the child lock on the back of the door frame.
Is this a sign of actuator failure or could it be the lock or latch that's seized? Is there any way to test it?