Hi all. I have a 2002 silverado 1500HD. My 4wd actuator on the front diff engages and then dissengages when I press the 4hi button. I replaced the actuator with a new one and replaced the in dash switch. The 4 hi light blinks and goes back to 2hi every time. When I push the auto 4wd the actuator seems to stay engaged. It is showing a service 4wd message. I've cleaned the grounds on the frame, but would like to see if there's any knowledge out there before I take it in for diagnostic.

 

The last time this happened to me , a 2002 Suburban, it was a encoder motor on the TC. I replaced it with a used one from auto wreaker.