Principles of Operation

Principles of Operation
The ABS module receives wheel speed readings from each wheel speed sensor and processes this information to determine if an ABS event is necessary. The wheel speed sensors are ACTIVE, and switches the voltage between high and low to give a square wave signal. The sensor can read down to zero mph. The wheel speed sensor is imbedded in the wheel bearing seal. The seal is identified by the black coloration (a non-ABS wheel bearing has a red seal on both sides, an ABS bearing has a red seal on the non-sensing side, and a black seal on the sensing side). The rear wheel speed sensor ring is a steel annular ring pressed onto the hub assembly. The teeth are not visible to the naked eye.

The ABS module continuously monitors and compares the rotational speed of each wheel. When the module detects an impending wheel lock, it modulates brake pressure to the appropriate brake caliper by triggering the Hydraulic Control Unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to the desired speed, the ABS module returns the solenoid valves to their normal position and normal base brake operation resumes.

The ABS module is self-monitoring. When the key is turned ON, the ABS module will carry out an electrical continuity check. At approximately 20 km/h (12 mph) the pump motor is turned on for approximately 0.5 second and a dynamic wheel speed sensor check is carried out.

Note: If an acceleration of above 0.3g has been monitored by the system during the drive up to 20 km/h (12 mph) the sensor check is delayed for two minutes.

Acceleration above 0.3 grams is likely if the vehicle is being driven on an icy or snowy surface, or during a rolling road test. The ABS warning light will not illuminate and the ABS function is maintained. Also, during all phases of operation the ABS module (after the vehicle is in motion) checks for correct operation of the wheel speed sensors. Any failure of the ABS system will cause the ABS to become inoperative, however, normal power-assisted braking is maintained.