You will need to have the engine scanned by a repair shop. That will give them codes to repair it. Once repaired they will clear the light. Clearing the light does not repair the problem. ***See discussion area for my dispute of this above answer****
My 95 Astro did the same thing. It was a ton of carbon buildup on the catalytic converter which gunked up and messed with the oxygen sensor. The root cause was the fuel distributer had a pin-hole in it . The egr valve then also got all messed up.