Low beam, high beam

Low beam and high beam light up the road in front of the vehicle.

The following functions - depending on vehicle equipment and coding - can be implemented:

• Manual headlight vertical aim control in the case of halogen headlights
  
• Automatic, dynamic beam vertical aim adjustment in the case of xenon headlights: the automatic headlight vertical aim control is legally prescribed in the case of xenon headlights according to ECE regulations. The dynamic beam vertical aim adjustment optimizes the automatic headlight vertical aim control depending on load conditions of the vehicle (braking, accelerating).
  
• Automatic Light Control (depending on vehicle equipment, vehicle-specific coding and/or country variant)
  
• Home lighting
  

Brief description of components

Light switch

The light switch consists of

• Rotary switch for sidelights and low beam (and special equipment Automatic Light Control)
  
• Two buttons for fog lights and rear fog light
  
• Potentiometer for dimmer of panel illumination
  
• Potentiometer for manual headlight vertical aim control in the case of halogen headlights
  

The rotary switch for sidelights and low beam has two switch contacts. Depending on the status of the two switch contacts, the light module can detect four switch positions:

S_SL = interior switch for sidelights

S_AL = interior switch for low beam

1 = interior switch closed (after 5 V)

0 = interior switch open

Depending on the vehicle equipment and country variant, different light switches are fitted:

• Switch for vehicles with xenon headlights and automatic beam vertical aim adjustment (LWR),
  
• Switch for vehicles with halogen headlights and manual beam vertical aim adjustment (LWR), This switch has a potentiometer for manual headlight vertical aim control (can be operated using a knurled adjuster).
  
• Switch for vehicles with Automatic Light Control. The rotary switch has an additional switch position FLC for the Automatic Light Control as well as a light emitting diode.
  

Power supply: The switch is supplied with 5 Volts by the light module.

If the power supply is defective, the light remains ON:the light is automatically switched on if

• the cables to and from the light switch have been cut or
  
• are switched to earth
  
• are at 12 V.
  
• For safety reasons, the light switch can only be switched OFF if there is 5 V at both switch outputs to the light module. If a short circuit means that there is once 5 V and once 12 V, the light can not be switched OFF: low beam and Automatic Light Control remain ON.
  

Turn indicator-low beam switch

The steering-column lever to the left of the steering wheel switches the functions

• Turn indicator (one-touch flashing or continuous flashing left or right) with terminal R On,
  
• Parking light left or right: with terminal R OFF, overpress the switch beyond the engaging point, as for continuous flashing.
  
• High beam and headlight flasher.
  

The steering-column lever no longer engages in the switch positions. The functions are operated by

• Touching the switch to move it forwards or backwards: high beam and low beam
  
• Touching the switch to move it to the right or left: one-touch indicating
  
• Overpressing the engaging point: continuous flashing
  

If the driver operates the steering-column lever

• a message is transmitted to the light module. Signal path: SZL (steering column switch centre) -> data bus BYTEFLIGHT -> SIM (Safety and Information Module) -> data bus BYTEFLIGHT -> ZGM (Central Gateway Module) -> data bus K-CAN SYSTEM -> LM (Light Module).
  
• At the same time, the light module evaluates a direct signal from the steering-column lever. This signal is transmitted across a separate cable, making it independent of the K-CAN SYSTEM data bus.
  

Function limitation in the case of failure of the data buses:

• High beam and headlight flasher only run if the steering-column lever is held.
  
• The indicator light only runs if the steering-column lever is held. no continuous flashing, no automatic reset
  
• No hazard-warning lights in the event of a crash and when arming the anti-theft alarm.
  

Light module

The light module controls and monitors the vehicle lights. Information is received and sent via the data bus K-CAN SYSTEM.

In the case of the special equipment xenon headlights, the defects of the xenon headlights are evaluated in the light module.

Emergency operation properties of the light module: The light module is supplied with terminal 30 twice.

If a terminal 30 fails, the following are activated:

• Front lighting: low beam and parking light (each on one side).
  
• Rear lighting: On one side, the outer sidelights/brake lights are activated. On the other side, the inner taillights are activated. The vehicle thus still has lights on both sides. Confusion with a one-track vehicle (motorcycle) is excluded.
  
• Brake light: One side of the brake lights is activated with normal power (ECE coding). This leads to ”one-track” braking, as if for example one brake light had failed.
  

In the case of a failure of the processor, emergency operating mode is activated. Emergency operating mode involves hardware that is completely independent of the light module. Emergency operation properties with failure of the processor:

• Vehicle lighting: At terminal 15 On, the following are switched on: Front low beam and outer rear sidelights / brake lights left and right. The outer sidelights / brake lights left and right are not, as would be normal, dimmed to 10% of their brightness, but operated with full power. This ensures the function of the vehicle lighting irrespective of the position of the light switch.
  
• Brake light: With terminal 15 On, the left and right brake lights are switched on when the brake-light switch is operated (via a hard-wired, direct line from the brake-light switch to the lamp drivers).
  

Function defects with failure of the processor:

• No turn indicators and hazard warning lights, no high beam, no headlight flasher, no fog lights, no rear fog light, no third brake light
  
• No communication across the K-CAN SYSTEM.
  
• No communication with the trailer module
  

Halogen headlights

Depending on model of vehicle, halogen headlights or xenon headlights are fitted.

Xenon headlights

Xenon headlights consist of

• headlights with D2-S bulb (bulb with a xenon gas charge. (gas is ignited by a light arc),
  
• an electronic control facility (ignition device and control unit).
  

The xenon headlights of the E65 have additional mechanical panel shutters in front of the light units. These shutters are electromagnetically adjustable. The shutters regulate in two stages the light beam of the low beam:

• Low beam: The shutters in front of the light unit create the legally prescribed shutter angle of the low beam.
  
• High beam: When the high beam is switched on (halogen headlights), the switching unit for the shutters is also switched on. The shutters are opened. This provides additional dipping of the low beam.
  

Electrical control facility for xenon headlights

The electronic control facilities for xenon headlights consist of

• xenon control unit and
  
• xenon ignition device. The ignition unit generates the high voltage necessary for igniting the electrical arc in the lamp.
  

The electronic control facilities for xenon headlights have self-diagnosis capability:

Diagnosis in the case of a defective xenon headlight:in the diagnostic mode, the light module supplies an auxiliary voltage to the xenon control unit. The xenon control unit replies with a morse code. This signal goes via the power supply line to the light module. The light module routes the fault message across the K-CAN SYSTEM directly to the diagnostic calculator.

Diagnosis in the case of a defective electronic control facility:if the electronic control facility for the xenon headlights is defective, the light module in the diagnostic mode receives no signal. The light module thus detects that the electronic control facility itself is defective.

Potentiometer for manual headlight vertical aim control

The potentiometer for manual headlight vertical aim control is fitted in the light switch. The potentiometer is operated by means of a knurled adjuster. This potentiometer specifies the height of the headlights. From this, the light module calculates the adjustment steps for the servomotors. There is no dynamic adjustment of the vertical aim to the relevant driving condition (accelerating, braking).

Ride height sensor for automatic headlight vertical aim control

The height sensors provide the light module with the input variables for the automatic headlight vertical aim control.

The height sensors are fitted at the front and rear:

• Front axle: the height sensors are on the wishbone. On spring deflection, the output voltage of the height sensors increases. On rebound, the output voltage of the height sensors decreases.
  
• Rear axle: the height sensors are fitted on the stabilizer link. On vehicles with pneumatic suspension, the signal of the left-hand ride height sensor is evaluated for the beam vertical aim adjustment: on rebound, the output voltage of the height sensors rises.
  

The light module uses the differences between the input signals of the front and rear height sensors to calculate the inclination of the vehicle in relation to the horizontal. The vertical aim of the xenon headlights are correspondingly regulated automatically and dynamically:

• Vehicle lower at rear than at front: vertical aim is shortened to legally prescribed vertical aim.
  
• Vehicle horizontal: vertical aim corresponds to the legally prescribed vertical aim.
  
• Vehicle lower at front than at rear: vertical aim is increased to legally prescribed vertical aim.
  

LWR stepped motors for headlight adjustment

For the beam vertical aim adjustment (LWR), LWR stepped motors move the headlights into the desired position. The LWR stepped motors of the headlights are activated

• manually depending on the potentiometer in the case of halogen headlights; signal path: potentiometer of the manual beam vertical aim adjustment -> light module -> step motors of halogen headlights;
  
• automatically by the light module in the case of xenon headlights, depending on the input signals of the height sensors.
  

When the light is switched on or the engine is started, a reference run is carried out: the headlights move to a defined initial position.

Rain/driving light sensor for Automatic Light Control

The rain/driving light sensor is attached to the windscreen.

The rain/driving light sensor senses

• the rain intensity to control the wiper intervals and
  
• the surrounding brightness for control of the Automatic Light Control.
  

The rain/driving light detects the surrounding brightness via two phototransistors:

• The surrounding light sensor registers the lighting intensity of the environment around the vehicle.
  
• The front light sensor registers the lighting intensity in a narrow corridor directly in front of the vehicle.
  

An internal processor uses the measurement data to calculate the required low beam.

When the light switch is in the position ”Automatic Light Control”, the low beam is switched on. The rain/driving light measures the surrounding brightness. If there is sufficient surrounding brightness, the rain/driving light transmits the command ”switch off low beam” to the light module. Signal path: Rain/driving light -> data bus K-CAN SYSTEM -> light module.

The internal calibration values of the rain/driving light must be matched with the windscreen type of the vehicle. If a new windscreen is fitted, the rain/driving light must be recoded for this windscreen.

Main functions

Manual headlight vertical aim control

In the case of halogen headlights, vertical aim of the headlights is set manually: Signal path: potentiometer of the manual beam vertical aim adjustment -> light module -> step motors of halogen headlights;

headlight vertical aim control

The automatic and dynamic beam vertical aim adjustment is calculated by the light module depending on

• Load status of the vehicle: in the case of xenon headlights, the low beam must not exceed a legally prescribed vertical aim. If the vehicle is carrying a heavy load (above all in the rear), the vertical aim of the xenon headlights must be reduced automatically to the legally prescribed vertical aim.
  
• Load to which vehicle is subjected: If the vehicle, e.g. in the case of heavy braking, is briefly lower at the front than at the rear, the vertical aim of the xenon headlights is increased. This means that the forward area is well lit up even during this brief dip of the vehicle.
  

Automatic Light Control

The option Automatic Light Control must be coded (Car and Key Memory).

If the Automatic Light Control is coded, the sidelights and low beam are automatically switched on under the following conditions:

• dusk
  
• darkness
  
• driving into an underground car park
  
• driving through a tunnel
  
• rain (as of a defined wipe frequency of the wipers)
  
• snow (as of a defined wipe frequency of the wipers),
  

When the ignition is switched off and the identifier key is removed, the exterior lights go off.

If only the sidelights are to be switched on, the light switch must be set to sidelights (1st switch position).

Home lighting

When the driver parks the vehicle and presses the headlight flasher, the low beam lights up for a brief period. This function can also be deactivated by coding the light module.

High beam and headlight flasher

The high beam and headlight flasher are produced by halogen headlights and added to the low beam.

Service functions

Note on safety

Xenon headlights: The relevant safety and accident prevention regulations must be observed when conducting all tests and work on the turn indicator-low beam switch / headlight system. The turn indicator-low beam switch / headlight system carries dangerous high voltages.

Country-specific version

USA

The manual headlight vertical aim control is not permitted by law in the USA. Vehicles with halogen headlights have no beam vertical aim adjustment.

Northern Europe: daytime driving lights of the low beam

Depending on coding of the light module, the daytime driving lights function can be selected (Car and Key Memory): low beam and sidelights are always switched on.

If the option daytime driving lights is coded, the light switch can always remain in the low beam position (2nd switch position). When the ignition is switched off and the identifier key is removed, the exterior lights go off.

If only the sidelights are to be switched on, the light switch must be set to sidelights (1st switch position).