I have a strange power lock issue with my driver side door. The power lock works fine when you use the button to lock it, but when you go to unlock it via the power unlock button, it doesn't work. All the other doors unlock, but the driver side door power lock does not activate. I have replaced the combination door latch/power lock assembly, and it still doesn't work.

So to trouble shoot this issue, I am trying to understand exactly how the power locks work. Here is what I have come up with so far...
1. The unlock button is pushed on one door modules.
2. The door module send a the unlock signal to the body control module (BCM)
3. The BCM triggers unlock relay?
4. ???
5. Profit!

If I can figure out how the unlock signal gets from the BCM to the lock (I suspect it goes back through the door module, but why use a relay??) Then I can try to figure out what to trouble shoot next.

 

1. The unlock button is pushed on one door modules (ie. DDM).
....1a. The door module unlocks this door.
2. The door module sends the unlock signal to the other door module (ie. PDM)
....2a. The door module unlocks this door.
3. The door module sends the unlock signal to the body control module (BCM)
....3a. The BCM triggers rear door unlock relay.
....3b. The relay unlocks the rear doors.

The relay is used to provide enough power to work all 3 rear doors at the same time.
Does the driver door unlock with the key fob? If, Yes, the door lock actuator and the DDM connections are OK, and the problem may be in the drivers door module (DDM)

 

Ok, now I think I am getting somewhere. The key fob (when it worked) never unlocked the driver side door. When the battery died in the fob, I was not able to re-program it because the driver side lock would not work. So this seem to be pointing towards the driver side DDM as causing this issue.