Brake light

At "Terminal 15 on" status the brake light can be activated by the brake-light switch. The Car Access System (CAS) furnishes the brake-light switch with a 5-volt voltage supply. The Car Access System (CAS) processes the status of the brake-light switch and transmits it through K CAN2. The footwell module (FRM) receives the status in this process and responds by activating the brake lights.

The signal from the brake-light switch is also employed by the dynamic headlight beam throw adjustment.

The brake light can also be activated by Dynamic Brake Control, such as the Active Cruise Control with Stop & Go function.

Dynamic brake light for European national-market versions 

In Europe, a new regulation prescribing dynamic brake light featuring an "emergency stop" signal is now in effect. The signal consists of:

• Flashing brake lights
• Activation of the hazard warning flashers

Operation of the dynamic brake light is divided into several phases:

• Normal braking
• Dangerous or emergency braking
• Activation of the hazard warning flashers
• Resetting the hazard warning flashers

Normal braking 

The footwell module (FRM) receives the signal from the brake-light switch directly. The brake lights are activated. The deceleration rate lies between 0 and 6 meters per second² .

The braking deceleration is monitored by wheel speed sensors. The Dynamic Stability Control (DSC) system transmits the wheel speed signals to the Integrated Chassis Management (ICM). The Integrated Chassis Management (ICM) then calculates the progression of the deceleration process as well as the speed. The Integrated Chassis Management (ICM) transmits the information over the FlexRay system. The central gateway module (ZGM) transfers this information to K CAN2. By this route the footwell module (FRM) receives the information for subsequent processing and analysis. The analysis is employed in generating the signals that control activation of the brake lights.

Dangerous or emergency braking 

The brake lights change from continuous lighting to a pulsed flashing mode under the following preconditions:

• Dangerous or emergency braking of sufficient duration
• Deceleration rate in excess of 6 meters per second²
• Closed-loop control intervention from the Antilock Braking System (ABS)

The brake lights then receive a control signal with a frequency of 5 hertz. The dynamic brake light functionality can be implemented at speeds of more than 50 kilometers per hour.

Activation of the hazard warning flashers 

The brake lights revert from their pulsed flashing mode to continuous lighting under the following preconditions:

• Deceleration rate falls below 2.5 meters per second²
• Driving speed drops below 20 kilometers per hour

The hazard warning flashers are automatically activated at the same time. This serves as supplementary warning source for following traffic.

Resetting the hazard warning flashers 

When the vehicle comes to a standstill, the hazard warning flasher remains on until the vehicle accelerates again or the hazard warning flashers are switched off manually.

Decoding the dynamic brake lamps 

Legal regulations in some countries prohibit flashing brake lights, which are therefore not included in the national-market versions for these countries. The "dynamic brake light" function is encoded to remain inactive in national-market versions destined for sale in these countries.

Brake Force Display (US national-market version) 

The Brake Force Display is fitted to vehicles for the US national-market version. Progress of the braking process is signalled by a corresponding enlargement of the surface area illuminated by the brake light. Flashing of the red surfaces on the brake light is not approved.

The Brake Force Display function operates under the following preconditions:

• Driving speed greater than 5 kilometers per hour
• Braking deceleration exceeds 5 meters per second2
• Closed-loop control intervention from the Antilock Braking System (ABS)