Ive got a 2009 Avalanche with intermittent door lock response on drivers side rear door. Regardless of whether I use the fob or the drivers door lock button, the rear door sometimes does not lock when activating the control. Any help would be appreciated! Thanks...

 

Sounds like you have a bad electrical wire running to that side. Either you have an open or shorting somewhere. I would pull the door panel and check the wiring. If it looks ok. You could have a bad input leading into the door lock.