My airbag light came on will GM replace this at no cost to me?

The airbag light coming on means the computer see's something wrong with the system and it needs to be diagnosed. The first step is to retrieve the trouble code that the control module has set and then the tech has to test the circuit that the code was generated for the same way that the module tested the circuit. It is unlikely that this is going to be for free and it is up to you to have the system repaired ASAP because it is a safety system.