Check Engine Lamp (MIL) Activation

PRE OBD II SYSTEMS

All M1.x and M3.x systems control the Check Engine Lamp in the instrument cluster. Faults that affect the mixture will cause the lamp to illuminate. When the engine control module detects an emission related fault, the final stage control for the lamp is switched on. Preliminary checking of the fault can be carried out through a flash code of the lamp or displayed with the MODiC or DIS tester. Refer to repair manuals or SI bulletins for flash code display procedures.

OBD II COMPLIANT SYSTEMS







The criteria for Check Engine Lamp illumination changed with the introduction of OBD II regulations. All M5.x and MS41.x systems comply with these regulations. The lamp is now strictly a warning device for an emission related fault. There is no longer any flash codes associated with the lamp for diagnostic purposes.

The number of monitored components has increased as well as the number of fault codes for various emission related components.

The total scope of monitored Systems has also expanded to include the transmission control module for any faults that might affect the level of exhaust emissions.

Check Engine Lamp illumination is dependent on the component or systems effect on the level of emissions. This includes fuel supply, fuel injection, ignition, idle control, coolant temp, exhaust and evaporative systems. Factors that influence OBD II monitoring include engine load, RPM, engine temperature and ambient temperature.

Components or systems that have a direct effect on emission levels will cause immediate illumination of the lamp. Other faults must be present for at least two start and stop cycles of the vehicle before the lamp will come ON.

If the lamp is "ON", a fault has been logged in the Engine Control Module memory for diagnosis and troubleshooting using the DIS tester.