my service engine soon light stays on on 2000 Oldsmobile Silhouette

my service engine light stays on. I have tightened by gas cap (maybe I need a new cap?). Could an additive to my gas make a difference. thanks

Asked by for the 2000 Oldsmobile Silhouette
This is the check engine light, and it's reacting to a fault in your emissions control system. If the gas cap doesn't resolve the light, it will be something else, and you'll need diagnosis. A fuel additive is extremely unlikely to make a difference.