Brake light switch: Function

The brake light switch is mounted on the brake pedal. It is in the form of a Hall-effect sensor. The switch is supplied with power by the light module as of terminal R ON.

The brake light switch is evaluated by the following control modules:

• Digital Motor Electronics (DME)
• Light module (LM) for activating the brake lights
• Car Access System (CAS) for enabling engine starting and forwarding the brake signals to the K-CAN BUS
• Dynamic Stability Control (DSC) for deactivating cruise control when the brake is applied

The brake light switch supplies two signals:

• S_BLS... Brake light switch
• S_BLTS... Brake light test switch

These signals are received and evaluated by the individual control modules independently of each other:

This ensures that the "Brake applied" signal is transmitted even in the event of a fault in the signal path.

In contrast to the other control modules, the two signals of the brake light switch are simultaneously evaluated in the DME. This direct comparison of the two signals makes it possible to establish definitely whether the brake pedal is being operated.

Furthermore, a malfunction of the brake light switch can also be diagnosed. In addition, the function is still possible if one of the signals fails.

The two signals of the brake light switch behave with respect to each other in accordance with the following table:

The following signal levels can be measured at the two outputs of the brake light switch: