My 2004 surburban has a service four wheel drive light on. The other day i was driving in 2wd and the truck just all of a sudden wouldnt move like it shifted to neutral on its on. The only way to get it to drive was to put it in auto 4 wheel. Can anyone tell me whats wrong?

 

Transfer case encoder motor. Been there, done that. Easy to install, but buy only the OEM or you'll be doing it again in 3-6 months.

 

i'd check your fluid level and condition before throwing any parts at it and get the code if you can