Brake Light Switch

Brake Light Switch

Brake light switch
Two Hall effect sensors as switches are installed in the brake light switch: the brake light switch and the brake light test switch (redundancy for safety reasons). The signals indicate whether the brake pedal has been pressed. The data interchange is digital.

Functional description
The brake-light switch has no moving parts and works as a non-contact switch. A change in the switching state is achieved by removing or applying a ferromagnetic trigger element to the brake pedal.
Switching mode with brake not applied: Brake light switch output conducts and brake light test switch blocks.







The two redundant signals from the brake light switch are read in by the Car Access System (CAS). The CAS forwards the signals on the bus system, e.g. for the engine control system.
The signals from the brake light switch are hard-wired and branched off for the following systems:
- Footwell module (FRM) for reversing light
- Dynamic Stability Control (DSC) for brake intervention
Included as of F1x: No longer hard-wired, rather bus signal to the DSC.

Structure and inner electrical connection
The Hall IC and magnet are arranged in a fixed position in the switch housing. No restoring force for the brake light switch has to be applied by the brake pedal.
The Car Access System (CAS) supplies the brake light switch with voltage (terminal 30B).







Electrical power supply and specifications
Terminal 30B definition for basic operation:
Supply of energy to components required when the driver is present. Activated by driver action (lock activation, opening the door, etc.). Deactivation following shutdown phase (1 to 30 min. depending on status).

Observe the following nominal values for the brake light switch:

Size Value
Voltage range 6 to 16 V
Current consumption in normal ≤ 8 A
operating mode
Output resistance, switch blocks 1.5 MOhms
Temperature range -40 to 85 °C

Diagnosis instructions

Failure of the component
If the brake light switch fails, the following behavior is to be expected:
- Fault entry in the Car Access System (CAS)
- Fault code memory entry in the Dynamic Stability Control (DSC)
Included as of F1x: no longer hard-wired, rather bus signal to the DSC.
- Fault entry in the footwell module (FRM)
- Fault code memory entry in the engine control system due to missing message on the bus system

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.