Non-OEM Parts

All of the OBD-II diagnostics have been calibrated to run with OEM parts. Accordingly, if commercially sold sensor or switch is installed, it makes a wrong diagnosis and turns on the check engine lamp.

Aftermarket electronics, such as cellular phones, stereos, and anti-theft devices, may radiate EMI into the control system if they are improperly installed. This may cause a false sensor reading and turn on the check engine lamp.