passenger air bag is off warning light why

Thank you Mikes. no there was nobody sitting in the seat, nothing on the seat,, just empty. I have never noticed the light before. I have the redlight seatbelt icon on the dash gauge which appeared just after being bumped while at a stop light and a car turning the corner hit my drivers front end. No air bags deployed and nobody in the seat at that time. The light has been on for almost 4 months. Thank you. Mikes Garage in Phoenix