Acura 3.5 RL Manual page 838

Wheel Speed and Modulator Control
SPEED
PRESSURE
OUTLET
VALVE
INLET
VALVE
MOTOR
ON
OFF
When the wheel speed drops sharply below the vehicle speed, the inlet valve closes to retain the caliper fluid pressure.
When the wheel speed drops further, the outlet valve opens momentarily to reduce the caliper fluid pressure. The pump
motor starts at this time.
As the wheel speed is restored, the inlet valve opens momentarily to increase the caliper fluid pressure.
Wheel Sensor
The wheel sensors are the magnetic contactless type. As the gear pulser teeth rotate past the wheel sensor's magnetic
coil, AC current is generated. The AC frequency changes in accordance with the wheel speed. The ABS control unit detects
the wheel sensor signal frequency and thereby detects the wheel speed.
GEAR PULSER
VEHICLE SPEED
REFERENCE VEHICLE SPEED
WHEEL SENSOR
WHEEL SPEED
TIME
at HIGH SPEED
at LOW SPEED