4X4 not working parts needed to check be found

I had the same problem the 4wheel ligths will shift from hi to lo and I heard the gears shitfing when I put it and gear. I just got it out the shop this week it was the transfer case motor it was shorted out from a wire harness that control the 4 wheel buttons I replace that switch and new motor its runs fine now it cost me 800 hundred dollars. Try changing that switch first its the cheapest than if that don t work hope its just the trans motor.I thought it was the trans and that would have cost me much more money good luck.

My vehicle is a 2002 Jimmy. If I engage the 4 wd on the fly at speeds greater than approx 30 mph, sometimes what happens is that the next time I try to go into 4 hi after shutting it off, it will not work. What I was told to do by a former GM mechanic is to disconnect the battery for 20-30 secs to reset computer. This worked on the 3 occasions where I had this problem. Now I only swith to 4 Hi at low speeds or else at stop signs or street lights. Hope this helps somebody.