Review Of Check Engine Light On But Car Is Running Fine References. Loose or faulty gas cap your gas cap is part of a sealed evaporative emissions system that recirculates gasoline vapors from your gas tank and keeps them from escaping into the air. To diagnose the check engine code, the first step is to check for common known problems.

If there is a problem with the car, it's probably the o2 sensor. A reader will cost you about $60.00. Faulty mass airflow sensor 6.
