OBD II Serviceability Issues
General Service InformationServiceability Issues
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.
Poor Vehicle Maintenance
The sensitivity of OBD-II diagnostics will cause the check engine lamp to turn on if the vehicle is not maintained properly. Restricted oil filters, fuel filters, and crankcase deposits due to lack of oil changes or improper oil viscosity can trigger actual vehicle faults that were not previously monitored prior to OBD-II. Poor vehicle maintenance can not be classified as a non-vehicle fault, but with the sensitivity of OBD-II diagnostics, vehicle maintenance schedules must be more closely followed.
Related System Faults
Many of the OBD-II system diagnostics will not run if the ECM detects a fault on a related system or component.