HELP!! 99 Silverado 4x4 not working

I have a '99 silverado with the autotrak nvg 246 t/c. My four wheel drive quit working the other day. The led in the dash indicates that it is in 4wd and I could hear the transfer case switching gears but no 4wd. So I checked the front differential actuator and it was operating. I then put my truck on jackstands (all four wheels off the ground) put it in 4wd and in neutral and turned the ignition on and tried to spin the rear wheels. When I did this the front wheels also turned, however when I let the front wheels down on the ground and tried to spin the rear wheels (still in 4wd) I could. What should be my next step of diagnosis?


New symptoms: T/c is stuck in 4hi when ever i go to select 2hi or 4lo I can hear the motor and encoder moving but no actual switching of the gears. If i press auto the encoder will move and the led changes to auto, and I can go back to 4hi. If i am in auto and try to go to 2hi the motor sounds like its moving and then all the indicator lights go out and the in dash display says service 4wd.

Well I'm no expert and it's been a while since I've had a 4x4 but if power isn't making it to the front wheels then your problem is with the transfer case. I don't know what that autotrac case looks like but if it autotrac portion is not external then it sounds like you need to open it up and check the internal linkages. You didn't say whether or not the truck was actually in 4wd when the dash indicator was lit but the service light does indicate that there's something wrong enough in there to trip the logic. You would probably get a better answer if you were to post this in a truck forum like over at pickuptruck.com.