Turn Off "Check Engine" Light Parts might cause your check engine light on include: 1. Gas Cap 2. Oxygen Sensor 3. Air Fuel Ratio Sensor 4. Mass Air Flow Sensor 5. Ignition Coils 6. Spark Plug Wires 7. Spark Plugs 8. Thermostat 9. EGR Valve 10. Evaporatative Emission Canister Purge Valve (EVAP) 11. Catalytic Converter.