The brake light switch indicates brake pedal status to the ABS control unit. The switch is turned on when brake is depressed. The brake light switch is a normally-open contact which runs to battery voltage when active (brake depressed).
The brake light signal is a reference to judge driver's intention for braking and The HECU checks open or short circuit of brake light switch for normal ABS/ESP control.
If an error is present, the warning lamp will illuminate.
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage monitoring
Open circuit in brake switch line
Faulty brake light switch
Case1
Monitoring
Period
Continuous (only no under voltage is detected)
Enable
Conditions
If the BLS-signals is high for 60 s at following condition.
1. the gas pedal is stepped
2. vehicle speed > 10.8km/h
3. offset compensated pressure < 5 bar
4. no control is active
Case2
Continuous (only normal voltage)
For redundancy reasons an additional BLSpVor-signal is created by the pressure sensor signal. If the pressure sensor is compensated, the threshold for generating the BLSpVor signal is 10 bar. If the pressure sensor is not compensated, the threshold is increased by 15bar. If this signal is set without any hardware-BLS-signals and if no pomp is operated during that time, a fault is set after the braking.
If the pressure signal is higher than 80bar and not both of the hardware-BLS are set, a fault is stored after 1s.
Fail-Safe
Inhibit the ESP control and allow the ABS/EBD control.
The ESP warning lamp is activated.
Brake Light Switch
Voltage Range of "High"
Voltage Range of "Low"
7.0V ~ 16.0V
0V ~ 3V