On a GM vehicle, the airbag light should come on for @ 6 seconds, and then go off if the system is working properly. If there is a fault or a problem in the system, the light will remain illuminated, or flash continuously. These systems can only be diagnosed using a scanner designed for the airbag system. The scanners at Auto Zone or the ones that sell for @ $50 will not access the airbag system, only the engine systems (check engine light).
Check out these websites for more info on airbag system.
http://blog.airbagsolutions.com/
http://www.airbagsolutions.com (Resource page is good)
http://www.airbagsolutions.com/scanner.aspx