2011 Chevrolet Traverse Air bag

Older cars just had an "Air Bag" warning light since Chrysler started using them in the late '80s. Your Air Bag Computer detected a problem, set a diagnostic fault code, and turned on the warning message to tell you. Your mechanic will start by reading the code(s). That will indicate the circuit or system that needs further diagnosis.

The cost is impossible to determine until the cause is diagnosed, but in general GM charges a lot more for their parts than most other manufacturers, and if a computer needs to be replaced it will have to be programmed to your vehicle by the dealer. They have many tricks built in to cost you money after the sale. Hopefully all you'll need is a sensor. Even those have been turned into complicated computer modules instead of the older inexpensive and very reliable mechanical switches but they aren't too expensive.