Malfunction Indicator Lamp: Description and Operation

Starting with 1996 model year, the criteria for Check Engine Lamp illumination is changed. OBD II regulations for emission control system monitoring have changed the criteria for lamp illumination. 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 now dependent on the component or systems effect on the level of emissions. This includes fuel supply, fuel injection, ignition, 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 MS41.1 Control Module memory for diagnosis and troubleshooting using the DIS tester. Fault Symptom troubleshooting should be used to troubleshoot problems with the MS41.1 system.

OBD II also requires that emission related faults be accessible through a separate diagnostic connector. This OBD II connector is only for use with an approved SCAN tool and related software. The OBD II scan tool and the BMW DIS tester operate independent of each other, consequently diagnostic data may appear different.