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Brake Fluid Level Sensor/Switch: Description and Operation

Brake Warning Indicator Switch
The brake warning indicator switch is a fluid level sending switch. The CAB sends out a 12 voltage signal to the switch. The switch has a 1,000 ohm (1K) resistor inside of it. This resistor is used for diagnostic purposes. Normal voltage is about 2.3 volts. If the switch is disconnected the resistor will be pulled out of the circuit and the CAB will sense voltage at about 5 volts. If the fluid level becomes too low or the circuit is shorted to the ground, the voltage will be about 0 volts. Any fault condition will illuminate the red brake warning indicator and the specific fault can be read on the DRB III.