Chevy Silverado 4wd issues

[Maxee08]

I recently lost 4wd on my silverado.  I have the 4 button automatic style and everything seems to function as it should.  The buttons light up as they should for 4hi and 4lo but when engaged the front tires dont receive power.  I put the rear tires on some ice and just let it turn the wheels slowly at an idle and was able to see that the front driveshaft was not spinning.  However when the car is put into the air on jack stands all of the wheels spin.  A couple days before I lost 4wd I had the "service 4wd" message pop up and the buttons didnt illuminate.  I turned the car off for about 30 minutes and it never came back and everything worked as it should.  The transfer case module didnt seem to have any codes.   I lost 4wd while pulling into my snowy driveway and about 5 feet in all of a sudden the rear wheels broke loose.  I just curious if anyone has heard of maybe the encoder motor not fully engaging 4wd or how to test for that before I pull the transfer case.

 

The truck is a 2003 Chevrolet Silverado 1500 z71 with g80 and 4 button automatic transfer case.