2006 Chevy Cobalt air bags

Electrical problem
2006 Chevy Cobalt 4 cyl Front Wheel Drive Automatic

HI, I have a 2006 cobalt and the air bag light came one and the code was b0013 (B0013 Driver Frontal Deployment Loop Stage 2 -SDM) what does this mean? Do I have to replace the front impact sensor? Or the actual air bag? I do not want to take it to the dealer unless I have to as there is no warranty left on the vehicle.