When the passenger seat is empty the warning light does not come on.
Why does my service airbag light come on when someone sits in the passenger seat on 2008 Chevrolet Cobalt
Your vehicle is equipped with an air bag system that has a sensor under the seats to calculate weight on the seat. This device helps the air bags deploy at different speeds based on the passenger’s weight or not deploy if no passenger is on the seat. This sensor is more than likely malfunctioning. Based on the year of your car, it’s probably still covered under warranty so call your favorite GM dealer and have them look at it for you.