Loose gas cap

The light coming on is just suggesting that you haven't tightened the gas cap, the actual engine code is the Evaporative Emissions System has detected a small leak, and 90% of the time, it's just because the gas cap is loose, but since you've already tightened it and it keeps coming back, try cleaning the o-ring in the gas cap itself, and if the code comes back, you'll have to get your Evap lines inspected with a smoke machine. But yes, a loose gas cap WILL set off a Check Engine Light. I'd try fixing the gas cap before getting too deep into it.