Lamp Control Module: Description and Operation

Lamp Control Module (LKM):

Functional Description:

General Block Diagram:

General:

The lamp control module (LKM) contains the relays for:
- Low beam
- High beam
- Rear fog light
- Fog light

In addition, the lamp control module LKM monitors the light circuits for failure of bulbs and breaks in wire connections. If a defect occurs in a circuit, the lamp control module (LKM) signals this status via the data link to the check-control module (CCM). The check-control module (CCM) transfers the message also via data links to the instrument cluster. A text note in the instrument cluster display informs the driver that the corresponding light has failed.

Warm/Cold Monitoring:

Light circuits are monitored by special electronic components, so-called comparitors. A differentiation is made between warm and cold monitoring.

Warm monitoring: The circuit is checked when the corresponding light is switched on.

Cold monitoring: The circuit is also checked when the corresponding light is switched off.

Scope of monitoring: A differentiation is made between the standard and luxury version. The luxury version is installed in the models 735 and 750i.

Light circuit Standard Luxury

Low beam warm/cold warm/cold
Front parking light warm warm/cold
Tail light warm warm/cold
License plate light warm warm
Fog light None warm/cold
Rear fog light None warm/cold

Rear fog lights are not installed in the country-specific version USA/Japan.

Brake Light:

An additional brake light test switch is necessary in order to monitor the function of the brake light. Shortly after operating the brake light switch, the test switch is switched on by the brake pedal. It switches ground to the check-control module. The circuit of the brake light, including the brake light switch is monitored for defects for as long as the test switch is switched on. A defect is indicated in the instrument cluster display unit.

The country-specific version USA additionally features a third brake light which is also monitored.

Parking Light Cold Monitoring Relay:

Cold monitoring of a light circuit is only possible when the light is switched via a relay. For this reason, the parking light and tail light are switched via the parking light cold monitoring relay (relay K7) in the models 735i and 750i. A jumper is installed in the 730 instead of the relay.