I have recently replaced both my rear door locks which would lock remotely but wouldnt unlock although you could hear the unit click as if it was going to work as they should. This has given me the oppurtunity to have a play on the bench with the old ones and have a good look at how the things work, Up until now the accepted approach seems to be "just replace them they cant be fixed". On examination i found both locks had a joint which was seized solid, The following pic shows the pivot (end of pencil) that is seized ,just behind it you can see the thread from a machine screw that limits its travel when its moving as it should. on examination its not seized through rust or dirt the machine screw has actualy tightened itself up and jammed it solid.
The second pic shows how to release it. All you do is close the striker which reveals a hole at the back ,this lines up perfectly with the machine screw head on the other side ,1/4 of a turn with a 4mm allen key and it frees it all up, on the drivers side its a left handed thread and on the near side its a normal right handed thread.
Heres the best part, you dont have to take anything apart to carry out this fix. Open the offending door, push the striker plate in as if its locked and you will see the hole in my picture, use a torch and you will see it lines up with the machine screw head, insert a 4 mm allen screw and slacken the screw 1/4 turn in the appropiate direction, pull the interior handle to release the striker, close the door and check if it works as it should, if not repeat with another 1/4 turn and check again.
Do not slacken any more than 4 whole turns as you run the risk of the screw coming out and requiring a strip down to replace it. IMO if it doesnt work after 1 whole turn you probably have a different fault.
This fix only relates to the rear doors
