2003 tahoe, rear doors/hatch dont always lock!

[Slammedchevy01]

Sometimes when I hit the lock button for my tahoe only the front doors lock and the rear doors/hatch stay unlocked. What is this caused by? I would say its my alarm but it started before that was installed. Any help would be great....just weird how it leaves all the rear doors open.

 

[Townsend600]

I had this problem once before and ended up using some graphite powder on the actuator. its plastic on plastic. Solved my rear hatch not locking.