I have a chevy blazer and the door locks are making me nuts... at first we thought maybe it was a fuse but DH checked both the fuse and the relay... basically the power locks will not lock properly. If you push the buttons its suppose to lock them but no it does not. Then DH thought maybe it was the motor for the power locks. But when ever you start the car it locks ALL the doors... and then when you park it unlocks them all. Very annoying to have to run around and lock all 4 doors when you are the only person in the car. Also the rear hatch never unlocks... so I have to put down and back seat and crawl into the back, not really the reason I have a hatch in the first place.

 

Well, maybe the switch on the drivers side is defective. My door doesn't seal well, so whenever it rains I grab a towel to make sure no water gets near that switch. Rust will prevent proper contact in switch.

There are good posts in the tech articles section on how to troubleshoot your rear hatch.
https://blazerforum.com/forum/articl...ailgate-35041/
https://blazerforum.com/forum/articl...ailgate-35041/