Could be a few things that I can think of;
1. Chafed wire under driver's seat (if the light goes off if you move the seat back and forth that's your culprit)
2. Airbag module (under center console, can go bad if something has spilled and found it's way under there)
3. Airbag fuse has blown out
4. Front impact sensors. I haven't seen it happen on these trucks, but I have had to replace them twice on my Avalanche due to GM's *strategic* placement of sitting under the bumper where all the rain, mud, salt etc beat the thing until it fails from corrosion.
INNOVA makes a good scan tool, I had an issue with the airbag light on in my old Envoy that turned out to be caused by a blown fuse and a flaky front impact sensor.