Anti-Lock Brake System (ABS)

The ABS module manages anti-lock braking, traction assist and roll stability control (RSC) systems to maintain vehicle control during deceleration, acceleration and vehicle maneuvers.

When the ignition switch is in the RUN position, the ABS module carries out a self-test by sending a reference voltage to each wheel speed sensor to determine if the sensors and related wiring are functional. At the same time, the hydraulic pump motor is turned on for approximately 1/2 second and the valves in the hydraulic control unit (HCU) are actuated to determine operational status of the HCU. Any malfunction of the ABS components disables the system and the ABS warning indicator illuminates. However, the standard power-assist braking system functions normally.

The active wheel speed sensor generates a signal that is sent to the ABS module. The wheel speed sensor circuitry connects to the ABS module through 2 wires and a connector at each wheel speed sensor. When the ignition is turned to the RUN position, the ABS module carries out a self-test to all of the wheel speed sensors through their circuitry to determine if they are functional.

The ABS module monitors and compares the rotational speed of each wheel through the use of active wheel speed sensors and wheel speed sensor rings. Wheel speeds are measured by the wheel speed sensor, which electrically senses each tooth of the wheel speed sensor ring as it passes through the magnetic field of the sensor. This information is sent back to the ABS module which is used to determine if a wheel lock is pending. When the ABS module detects an impending wheel lock, the module commands the HCU to activate the pump motor and to open and close the appropriate solenoid valves in order to modulate brake fluid pressure to the appropriate brake caliper(s). Once the affected wheel(s) return to the desired speed the ABS module commands the HCU to deactivate the pump motor and return the solenoid valves to their normal positions.