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Can you lock these doors from the switch, but not unlock them?
Dave, The locking problem is with the two rear doors and the rear gate that opens up from the rear bumper. The two front doors lock just fine. Here is what happens. If you try to lock the car from the interior from the drivers controls ( on the door) or by using the black keypad while outside the car, the 2 front doors lock just as they should but the other 3 doors ( rear 2 doors and tail gate) will not lock. They remain unlocked. When you try to open the two rear doors or the tailgate they do open, even though they are suppose to be locked and at the same time the car alarm goes off.
What you can do is lock the 2 rear doors mechanically by using the lock mechanism on each door rear door sepeartely. Then they are locked. The rear tail gate remains unlocked. Next when you use the black handheild keypad to open the car, all 4 lock doors open. Net - net --- the mechanically locks work and they also work via the electronics automaically when you use the key pad to open them. What seems to have happened is that the 2 rear doors and the tailgate seem do no be getting the electronic message to lock when you hit the black keypad nor will they lock when you try to do it from the drivers seat controls
Okay, your problem is a failed lock relay. This is a common problem. The lock relay operates the 3 rear doors. This relay is located in the fuse panel on the end of the drivers side dash. See picture below.
need help on a 1999 Chevy K3500 pickup with a 7.4 L