Antilock Brakes / Traction Control Systems: Description and Operation

Fig. 2 ABS Hydraulic Schematic (Part 1 Of 2):

The Anti-Lock Brake System (ABS) control module receives wheel speed readings from each brake anti-lock sensor. The module uses this information to compare wheel speeds. The anti-lock brake sensor electrically senses each tooth of the anti-lock brake sensor indicator as it passes through the anti-lock brake sensor's electrical field. This data is sent on to the ABS control module. The control module monitors the frequency created when the anti-lock brake sensor indicator teeth pass the brake sensor to determine wheel rotational speed.

By continuously monitoring and comparing each wheel's rotational speed,
the module activates the ABS only when it senses an impending wheel lock-up under severe braking conditions. During ABS cycling, a brake fluid pump motor recirculates the brake fluid.

The module then decides which wheels' brakes need to be controlled and
sends the appropriate signals to the hydraulic control unit (hydraulic portion of the assembly). Impending wheel lock conditions trigger signals from the hydraulic control unit which opens and closes the appropriate modulator solenoid valves. This may result in moderate pulsations in the brake pedal when applied. During normal braking, the brake pedal feel will be the same as a vehicle with a standard brake system.