if it has push button 4wd controls, gm had HUGE problems w/ the switch itself. will usually set a code and say service 4wd int the display in inst. cluster
If it is working it is OK, look elswhere for your problem, the transfer case might not be engaging but i can't help you with that.
Need to check the front4x4 actuator on the front housing to see if its working. there is a switch on the top of the transfur case that sends power to the front actuator to ingage 4x4
Need one hell of a lot more information then this
Could be the vacuum actuator, or it could be an electronic fault, if you have an electronically controlled transfer case or an all wheel drive vehicle.
Your 4WD is currently not working. There has been some problems with late model GM trucks 4WD. Some are related to the pushbutton switch on the dash. My 02 silverado was warrantied by dealer because of a bad dash switch. This just happened to me. I was told to check the fuse first, if it wasn't blown it would be in the switch. Sure enough the fuse was blown...replaced and now working fine. same thing happened to my 03 silverado 2500hd. its the 4wd actuator switch. i think there is a bulletin on this.
rpm and speedometer gauges not working 1995 Chevy silverado 2wd
Slamming the trunk lid can damage the actuator and keep it from pulling the trunk lid down. The actuator will probably need to be replaced.
There could be a blockage in your heater core, I suggest you get it flushed to see if there is flow through it.
An airscrew is a propeller of an aircraft, or an actuator disc whose working fluid is air.
Your door lock actuator is faulty and needs to be replaced
With a hanger
Blend door actuator failure.