To figure out what this is, you need to take the car to a dealer. a diagnostic needs to be done of your airbag system, often times a sensor goes bad, a diagnostic will tell you exactly what the problem is, a computer is plugged onto your car, it asks the air bag computer to run a diagnostic on itself, your car will tell the diagnostic computer what is wrong, and what needs to be fixed. The reason the air bag light is on, is this is to let you know the air bag is not working.