2005 Chevrolet Cobalt Cobalt

The actual problem is a large leak in the fuel vapor recovery system. Since the most common cause is a loose gas cap, they use that as the warning light. In fact, there's a number of other things that can cause the same leakage. That can be as simple as loose or rusted hose clamps or as hard-to-find as a leaking valve. If the cause can't be found with a visual inspection, your mechanic can use a smoke machine to inject a white, non-toxic smoke, then he watches for where it sneaks out.