2003 Chevy Tahoe 4 wheel drive

auot 4 wheel drive seems to be out. Worked fine yesterday but now nothing. Rear wheel drive works fine. Seems to be electrical. Press 4Hi button, nothing happens. Press Auto 4 wheel drive button, nothing happens. Is there a switch or fuse somewhere that I can replace or is it something more serious? Trying to get some idea before I bend over for the dealership. thanks