Hello and thank you for using JustAnswer. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.
This light being on can be due to a great number of things. There is a problem that is common to these trucks. It is a bad connection at the drivers side kick panel. Remove the drivers side kick panel and unplug the yellow connector and reconnect. Do this 3 times and then turn the key on again and see if the light is still on. If the light goes out then this connector will need to be replaced. If the light does not go out then you have another problem and you will need to have the airbag system scanned for trouble codes.