I have a 2006 GMC Sierra 1500 with 141k on it. About 10 days ago I was headed to work on icy roads, so I decided to put it in 4 hi. I first noticed that there was a terrible howling noise after 20mph ( I know it's not uncommon for there to be some noise like this, but this was terribly loud). Then I realized that even though it was showing 4x4, my front wheels weren't spinning. I replaced the front actuator on the transfer case, I can hear the transfer case engage but my front wheels dont spin in high or low. I have the auto 4 option, and the 4wd works when in that option, but I'm just perplexed why it wouldnt engage in his or low but it will in auto. Any suggestions?

 

do you mean the shift motor on the transfer case? did you check the fluid level and condition of the transfer case?