Not sure.... its my bosses truck doing it so Im going to take a look at which relays it could be in the under column relay panel, pull all related ones and go buy all news ones and try it! Ill let you know....
Replace them in pairs......don't ask me why but I had a problem with my rear door not unlocking and the problem DID NOT follow the relay. i.e. swapping the realy for the rear doors to the front, etc. Replace both front and rear relays and everything has been fine since.
We have had trouble with one of our trucks, the 04 GMC. Lock would work, unlock didn't. Found out that the button on the fob had to be held down much longer for unlock as compared to lock. Only one truck out of 4 seems to work this way.