Your GMC Safari may have failed the smog check for high HC due to a few different reasons. The main reasons vehicles fail for high HC is defective ignition components such as spark plugs, spark plug wires, defective ignition distributor, distributor rotor, and ignition coil. However you also want to ensure your GMC is in proper fuel control as well. A rich fuel mixture (as well as a lean fuel mixture) may cause high HC as well. It's best to have a smog check repair station conduct a fuel feedback test to ensure your Safari's engine is not running lean or rich.
Read more about High HC Faults here.
