what year monte carlo? is it the amber 'check engine light'?
The best (and cheapest) way would be to head down to your local auto zone. they will scan the computer for free, and tell you what the code is.Write down the code, have them clear the light, and let me know what the code is. The light is on for a reason, the car's computer has detected a system that is out of specification. We need to find out if the problem is serious or not.
unfortunately you did not put the full code in your post. If the code said small leak detected code 442 it could very well be a gas cap. I would make sure the gas cap is tight, and if the code comes back try a new one.
did they clear the light? did it come back right away? If it did come back right away, I will need the full code # XXXXX proceed any further