Brake light

The brake light functions in 2 stages: normal braking and strong braking. In the case of strong braking, the sidelights / outer brake light lamps are also activated (dependent on coding and country variant).

If the special equipment ACC (Adaptive Cruise Control) is fitted, the vehicle may be braked automatically. This braking is also signalled to following traffic by the brake lights.

Brief description of components

Brake light switch

The brake-light switch is an electronic switch. The brake light switch is supplied with power by the light module as of terminal R ON.

For safety reasons, the brake-light switch contains 2 switch outputs:

• One output is connected with the light module.
  
• A second output is connected to the CAS (Car Access System) control unit. The CAS evaluates the brake signal and passes the brake signal on to the K-CAN SYSTEM.
  

The signal ”brake-light switch operated” is thus received by two independent control units and passed on. If one of the two signal paths fails, the other still functions.

Light module

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

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
  

Brake lights

The brake lights are light emitting diodes (LEDs). The LEDs are not monitored by the light module.

Additional (centre) brake light

The centre brake light consists of light emitting diodes (LEDs). The LEDs are not monitored by the light module.

Sidelights / outer brake lights

The taillights and outer brake lights left and right are combined into one light. This light consists of light emitting diodes (LEDs). The LEDs light up in two different brightnesses, depending on function:

• Parking lights/sidelights: the light emitting diodes are activated with 10% of their power.
  
• Braking stage 2 (dependent on coding): in the case of strong braking, the LEDs are activated at 100% power.
  

The LEDs are not monitored by the light module.

Inner brake lights

The taillights and inner brake lights are also combined into one light. This light consists of light emitting diodes (LEDs). The LEDs light up in two different brightnesses, depending on function:

• Sidelights: the light emitting diodes are activated with 10% of their power.
  
• Braking stage 2: in the case of strong braking, the LEDs are activated at 100% power (EC coding).
  

The LEDs are not monitored by the light module.

Main functions

Normal braking: braking stage 1 (EC coding)

In the case of simple braking, the

• brake lights left and right, and
  
• centre brake light go on.
  

Strong braking: braking stage 2 (EC coding)

In the case of strong braking, the sidelights / brake light lamps are also activated:

• Sidelights / outer brake lights
  
• Inner brake lights
  

The braking stage 2 is activated

• when strong deceleration is detected or
  
• when an ABS intervention takes place (anti-lock braking system activated).
  

Country-specific version

USA

In the USA country variant, the two stages of the brake light are coded as follows:

• Braking stage 1: brake light and sidelights / outer brake lights
  
• Braking stage 2: brake light, sidelights / outer brake lights, and additionally inner brake lights
  

If a terminal 30 of the light module fails, the following are activated:

• brake light on one side of the vehicle
  
• outer sidelights / brake light lamp on the other side of the vehicle