I have a 2002 Silverado and the 4x4 isn’t working. I push the button and the 4x4 switch blinks for a few second and you can hear (and feel) the actuator click in below. Then it lights up in the proper 4x4 mode just like it should. All indications appear that it’s working… but it’s not. No service 4x4 codes or anything. Another thing… I turned the front drive shaft by hand… spins freely in 2hi like it should. Switched to 4L and the driveshaft locks down like it should. Again… everything seems to be working… just isn’t. I didn’t find out until yesterday when I got stuck… and couldn’t ever get 4x4 to work. Sucks because I was barley stuck and would have pulled right out if I had 4x4. What should I check? Also the ABS light is on in the truck…has been for a longwhile. I read somewhere that this can cause the 4x4 not to lock in ?? True? anyway to override the ABS?