4x4 stuck

Any suggestions on this?

Drove to work this morning ... in 2WD .. no problems. Went out for lunch and started it up, noticed it was in 4HI - and it won't shift out of it. I have a 2001 GMC Sonoma .. just over 52000 miles. The light for 4HI stays on, but when I press 4LO or 2WD, it won't switch out into anything else. I can definately feel that its in 4x4 by the way it drives. Any ideas what could cause this? I'm a first time 4x4 owner, so I'm freaking out that I'm gonna be spending a bunch of money on a new transmission or something ... c'mon guys, help relieve me a little!!

Thanks!

I had the exact same symtoms on my 1998 sonoma no codes were set narrowed it done to the encoder motor. purchased rebuilt one from Cardone, works great now.

I had a problem like that once and it was a blown fuse.