Extract from BMW WDS info about the Light Switch Module.
Light switch centre (LSZ)
In addition to the electronic control and monitoring system for the external vehicle lights, the light switch centre also comprises the switch for sidelights/dipped beam, the pushbuttons for fog lights and rear fog lights as well as the potentiometers for instrument locator lighting and manual headlight vertical aim control.
Scope of functions of light switching centre
Control and monitoring of the outer headlights and lamps, including the indicator and hazard warning flasher function
Control of relay for fog lights
Evaluation of load sensors for automatic headlight vertical aim control and the resulting activation of stepper motors of evaluation of potentiometer for manual headlight vertical aim control.
Dimmer function for instrument and locator lighting (terminal 58g) as well as the function and locator lighting for the hazard warning switch.
Communication with other control units and diagnosis takes place via the K-bus. The light switching centre receives information via this bus relating to the vehicle status and also provides information on the status of the controlled lamps (defective/OK, switched ON/OFF).
The indicator lamps for full beam, fog light, rear fog light and direction indicators in the instrument cluster are controlled by the light switching centre on the basis of K-bus telegrams.
Design
The light switch centre consists of a control unit and operating panel
Both units are interconnected by means of a plug connector.
Control unit
The control electronics is accommodated in the control unit.
Operating panel
The switches for sidelights/dipped beam, fog lights/rear fog lights as well as the dimmer for headlight vertical aim control and instrument lighting are integrated in the operating panel.
The operating panel can be replaced separately from the control unit.
If replacement is necessary, corresponding reference to this is made in the test module.
Lamp monitoring
The lamps are monitored in OFF and ON status.
Cold monitoring in the OFF status takes place by briefly switching on the lamp (so short that the lamp does not light up). The lamp current is monitored and an assessment is made as to whether the lamp is defective or not.
Note
If the battery voltage drops below approx. 9.5 V, the lamp status can no longer be monitored or output.
Activating indicator lamps in the instrument cluster
The indicator lamps for left direction indicator, right direction indicator, rear fog lights, fog lights, full beam as well as the LEDs in the pictogram incorporated in the instrument cluster are activated via the K-bus.
Emergency mode
Independent hardware is provided in order to maintain the functions necessary for driving safety in the event of the control unit failing.
If the light switching centre is in emergency mode,
Tail lights and dipped beam lights are switched on at terminal 15 irrespective of the position of the corresponding light switch
Left and right brake lights are switched on at terminal 15 and the brake light switch operated
Direction indicators, hazard warning lights, full beam, headlight flasher, fog lights and rear fog lights cannot be switched on.
Diagnosis is not possible
If in emergency mode, the light switching centre must be replaced.
