Driver & passenger doors lock & unlock with driver door button & key.
But, rear passenger and back hatch locks only lock with driver button...but wont unlock?? HELP

 

I can only relate on what happened to me. I bought a 2001 GMC Yukon XL last year with a few issues to sort out. The last one being the door locks. I could not for the life of me get the rear barn doors to lock / unlock. I tried everything, cleaning the contacts replacing the actuators.......no luck. Periodically I check all headlights, parking lights and brake likes etc. to make sure they work. I noticed one of the license plates lights was out. I replaced it. I went someplace and wanted to lock the car. I clicked the FOB and noticed the rear number plate lights flashed. I thought they have never done that while other lights did. Sure enough the barn doors locked.

I have no explanation of what happened. I have also been an electrician for 40 years. Somehow replacing the bulb completed a circuit someplace and the locks have worked from that day on.

Tom