Brake light switch

The brake-light switch serves to detect brake pedal operation.

Function

The brake-light switch is a Hall sensor fitted at the brake pedal. The switch is supplied with voltage by the light module as of terminal R ON.

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 units (choice, see table below) independently of one another:

The redundant signal ”Brake activated” as a directly wired signal and as a CAN message means that transmission is also ensured in the event of errors on a signal path.

In the engine management system, both signals of the brake-light switch are evaluated simultaneously. 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.

The two signals of the brake-light switch behave in relation to one another according to the following table:

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

Diagnosis

The signals of the brake-light switch are continuously checked by the engine management system as regards plausibility. In the event of errors, a fault is entered in the fault code memory of the engine management system. Cruise control is also deactivated at the same time.