Civic Si L4-2.0L (2004)
Wheel Speed Sensor: Description and Operation
Wheel Sensors
The wheel sensors are the magnetic contactless type. As the gear purser 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.
Wheel Speed and Modulator Control
When the wheel speed drops sharply below the vehicle speed, the inlet valve closes and if necessary, the outlet valve opens momentarily to reduce the
caliper fluid pressure. The pump motor starts at this time. As the wheel speed is restored, and the outlet valve closes, the inlet valve opens
momentarily to increase the caliper fluid pressure.