Non-OEM Parts

The OBD II system has been calibrated to run with Original Equipment Manufacturer (OEM) parts. Something as simple as a high-performance exhaust system that affects exhaust system back pressure could potentially interfere with the operation of the Exhaust Gas Recirculation (EGR) valve and thereby turn ON the MIL. Small leaks in the exhaust system near the post catalyst oxygen sensor can also cause the MIL to turn ON.

Aftermarket electronics, such as cellular phones, stereos, and anti-theft devices, may radiate Electromagnetic Interference (EMI) into the control system if they are improperly installed. This may cause a false sensor reading and turn ON the MIL.