When your “check engine” light is displayed it usually means the car’s emissions control system is faulty and the vehicle is polluting the air beyond allowable federal standards. A vehicle with this condition would likely fail an emissions inspection. Common causes include a gasoline cap that is loose, oxygen or mass airflow sensor is bad, spark plugs may be caking with too much carbon buildup, spark plug wires are bad, or the catalytic converter is faulty (rare). You should not confuse the “check engine” light with the maintenance or service light; those signal a more immediate condition and should be promptly diagnosed.