Poor Vehicle Maintenance
The sensitivity of OBD II diagnostics will cause MIL to turn on if vehicle is not maintained properly. Restricted air 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 sensitivity of OBD II diagnostics, vehicle maintenance schedules must be more closely followed.