Volkswagen Passat 2006 Service Training page 55

How it works:
On actuation of the brake pedal, the push rod in the
brake master cylinder pushes the piston with magnetic
ring (permanent magnet).
Brake pedal not actuated:
When the brake pedal is not actuated, the piston and
magnetic ring are at rest.
The evaluation electronics of brake light switch F
transmit a signal voltage of 0 - 2V to the engine
control unit and the vehicle electrical system control
unit. This is used to detect that the brake pedal is
not actuated.
Brake pedal actuated:
When the brake pedal is actuated, the piston is
moved over the hall sender.
When the piston's magnetic ring passes the hall
sender's switching point, the evaluation electronics
transmit a signal voltage, which is up to 2V lower than
the vehicle electrical system voltage, to the engine
control unit. This is used to detect that the brake pedal
is actuated.
Signal voltage to the
engine control unit
Signal voltage to the
engine control unit
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