How It Works

WARNING: This page does not describe the selected car, but rather 46 other vehicles, including the 2008 BMW M5, 2008 BMW 650i, 2007 BMW Z4, 2007 BMW M6, and 2007 BMW M5. However, it is still accessible from the selected car via links, so may be relevant.

The range of functions of the light module includes the following tasks:

Actuation of headlights and exterior lighting on vehicle
Cold monitoring and hot monitoring
Actuation and monitoring of the turn signals and hazard warning lights function
Dimmer for the instrument and locating lighting (terminal 58g) and the function and locating lighting for the hazard-warning lights switch
Evaluation of messages from the rain-light sensor for the automatic driving lights control and for the adaptive headlights
Communication with the trailer module, if fitted
Actuation of the green indicator lamp for the adaptive headlights (on light switch)
Data exchange via K-CAN (see below)
With option 522 "Bi-xenon dipped/main-beam headlights", the light module evaluates faults in the bi-xenon headlights.
Emergency-running characteristic (see below)

Actuation Of Headlights And Exterior Lighting On Vehicle All lighting loads are actuated by the light module:

Output limitation: If the on-board supply voltage exceeds an encoded value, the lights are dimmed to increase the service life of the bulbs. Each bulb (rear light, brake light etc.) has its own encoded value. The values are encoded during production at the end of the assembly line.
Reduced ON current: The light module switches on the individual lights one at a time to prevent the vehicle electrical system from being overloaded unnecessarily by voltage peaks and high currents produced when the lights are switched on.
Prevents light intensity fluctuations: Systems with a high current draw and short load peaks can cause voltage dips in the vehicle electrical system. These voltage dips can cause fluctuations in the intensity of the vehicle lighting. Corresponding parameters are stored in the light module to prevent visible light intensity fluctuations.

Cold Monitoring And Hot Monitoring The lighting loads are individually diagnosed via the light module as follows.

Cold monitoring: For cold monitoring, the lights are switched on briefly without the bulbs glowing (thermal inertia of bulb elements). Exception: LEDs and bulbs for the bi-xenon headlights are not cold monitored. This is because: LEDs respond too quickly. The bulbs for the bi-xenon headlights must not be actuated with voltage pulses on principle.
Cold monitoring starts when terminal 15 is switched ON. This pre-drive-check indicates the condition of the lights before the start of a journey (car symbol in Check-Control display). Cold monitoring detects either "light available" or "open circuit". The cold current is a multiple of the rated current.
Hot monitoring: The rated current of bulb when it is switched on is monitored via the status output of the lamp driver. A defective bulb can be detected within 2 seconds.
Frequency counters count how often a defect occurs. The defect will be reported when a certain frequency is exceeded. When the ignition is switched off, all frequency counters are reset to zero to prevent a bulb that has already been replaced from being indicated as still defective.

Data Exchange Via The K-CAN The light module receives the following messages via the K-CAN:

Terminal R On: Signals From Car Access System (CAS Or Ignition-Starter Switch)
2-Stage Brake Light
Side Lights
Dipped Headlights
Front Foglights
Rear Foglight
Ride-Height Sensors

If option 524 "Adaptive headlights" is fitted, the signals from the ride-height sensors are fed directly to the control unit for adaptive headlights.

Emergency-Running Characteristics The light module has the following emergency-running characteristics:

Power Supply Failure: The light module has two terminal 30 power supplies.
If a terminal 30 fails, the following lights will be actuated:
- Front lighting: Dipped headlights and side lights (one side of vehicle each)
- Rear lighting: The side lights and outer brake lights are actuated on one side (parking lights). The inner rear lights are actuated on the other side of the vehicle. The vehicle thus remains lit on both sides. It is thus impossible to confuse the vehicle with a single-track vehicle (motorbike). -
- Brake lights: The brake lights are actuated with normal brightness on one side of the vehicle (encoding-relevant "European version"). This allows "single-track braking", as if, for example, a single brake light had failed.
Processor Failure: If the processor fails, the system will switch to emergency operating mode. Emergency operating mode is a hardware feature and thus completely independent of the light module.
Emergency-Running Characteristics If The Processor Fails:
- Vehicle lighting: The following are switched on when terminal 15 is switched ON: At the front the dipped headlights, and at the rear the position lights and the left and right outer brake lights (side lights). The position lights and the left and right outer brake lights are not dimmed to 10% brightness, as is usually the case, but rather operated at full power. Vehicle lighting is thus assured, regardless of the position of the light switch.
- Brake lights: When terminal 15 is switched ON, the left and right brake lights are switched on when the brake pedal is pressed (via a direct wire from the brake-light switch to the lamp drivers).
Malfunctions In The Event Of Processor Failure:
- No Turn Signal, No Hazard Warning Lights
- No Main Beam, No Headlight Flasher
- No Front Foglights, No Rear Foglights
- No Additional Centre Brake Light
- No Communication Via The K-CAN
- No Communication With The Trailer Module