Lamp Control And Monitoring

Lamp control and monitoring on the E39 and E53 follow 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, high beam and fog lamp indicator illumination.
• The ZKE for crash alarm indication.
• The AGS (EGS) 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. This monitoring takes place in timed cycles.

• Hot monitoring takes place from the LCM by monitoring the current flow through the output stages. The current flow is determined by looking at the voltage drop of the circuit.
• Cold monitoring takes place by the LCM by briefly switching the lights ON using a small amount of current. The LCM uses this to measure the voltage drop of the circuit. The small amount of current is not enough to cause the lights to illuminate.