Light Check Module (LCM)

Light Check Module (LCM)












The Light Check Module (LCM) combines the functions of the Check Control and Light Modules previously installed in the 1995 E38. The new LCM provides a cost savings by combining the two functions into one processor.

It is installed in the right kick panel where the LM of the 95 E38 was installed. Both versions of instrument clusters use the LCM for processing Check Control data and controlling the exterior lighting functions of the vehicle. The LCM communicates with other modules over the "I" and "K" busses. Functions of the LCM include:

- Monitoring of all check control inputs
- Formation and output of check control messages or signals
- Control of all vehicle external lighting
- Monitoring of all external lighting for operation
- Instrument panel illumination dimming (KL 58g) signal
- Control of instrument cluster indicator lights - for high beam, turn signal and fog light indicators.

For proper operation of the check control and lamp control functions, the LCM must be coded with the Central Coding Key (ZCS) if replacement is required.

Lamp Control/Monitoring












Lamp control and monitoring on the E39 follows the E38 in design and function. All exterior lighting is controlled by the LCM. It contains transistor power output stages for activating the lights. This eliminates the need for fuses and relays previously used for this purpose.

The LCM receives the input request for light illumination from the various switches and data inputs from other control modules. The LCM then switches the power output stages ON for lamp activation.

Other control modules that communicate with the LCM include:

- IKE over the I/K bus for turn signal, highbeam and fog lamp indicator illumination.
- The ZKE for crash alarm indication.
- The AGS control module for back up lamp activation.

All exterior lighting is monitored (both hot and cold) by the LCM. When the monitored value exceeds an acceptable level (high or low) the LCM generates and sends the signal to the IKE or base instrument cluster for check control display.

- Hot monitoring takes place from the LCM by monitoring the current flow through the output stages.
- Cold monitoring takes place by the LCM by briefly switching the lights ON and monitoring the current flow through the output stages. This is not enough to cause the lights to illuminate.

For safety purposes, the LCM is designed with emergency functions. A LCM failure will still allow various lamps to function for safety purposes. These lamps include:

- Side marker/tail lights
- Low beam headlights
- Brake lights
- Turn signal lights