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 | Monitoring Period |
•
Continuous (only normal voltage) | |
Enable Conditions |
•
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 |
