Brake Fluid Pressure Sensor/Switch: Description and Operation

Pressure Switch Cut-Away View:

PURPOSE
The pressure switch monitors the pressure accumulation (pressure from the pump) in the accumulator and is turned OFF or ON when the pressure becomes lower or higher than a prescribed level.


LOCATION
The pressure switch is mounted to the modulator and located next to the accumulator. The modulator is mounted to the firewall at the left-hand side of the engine compartment.

OPERATION
The pressure switch acts as a pressure regulator for the ABS system. It monitors the pressure accumulation in the accumulator (pressure from the pump) and is turned OFF or ON (points of the switch are opened or closed) if the pressure becomes lower or higher than a prescribed level. The switch is turned OFF if the pressure becomes lower than a prescribed level, and is turned ON if higher than a prescribed level. When the pressure in the accumulator rises, the Bourdon tube in the pressure switch deforms outwards. When the free end of the Bourdon tube moves more than the prescribed amount, the micro-switch is activated by the force of the spring attached to the sensing lever. When the ABS control unit receives this signal, it de-activates the motor relay which (in-turn) de-activates the motor. When the pressure in the accumulator decreases due to anti-lock brake system operations, the Bourdon tube moves in the direction opposite to the one described above, and the microswitch is eventually turned off. Upon receiving this signal, the ABS control unit activates the motor relay to operate the motor.