ABS Components

The Saturn antilock brake system consists of two subsystems: a conventional hydraulic brake system and the antilock brake control system. The antilock brake control system consists of the following components: four wheel speed sensors, a motor pack assembly, a modulator assembly, two solenoid valves, an antilock brake control module, and interconnecting wiring.
^ Wheel Speed Sensors: These sensors provide a frequency and voltage signal that is proportional to the wheel speed. The sensor consists of wire windings wrapped around a magnet. A toothed (47 teeth) speed sensor ring (spinning at road wheel speed) interrupts the magnetic field created by the wheel speed sensor, alternately increasing and decreasing the strength of the field. This increasing and decreasing magnetic field creates a voltage and frequency signal in the sensor wire windings that varies proportionally to road wheel speed. This signal is used by the antilock brake control module to determine the road wheel speed.

On the front wheels, the speed sensor is fastened to the steering knuckle. The front wheel speed sensor toothed ring is pressed onto the end of the axle shaft assembly. On the rear wheels, both the wheel speed sensor and toothed ring are contained within the wheel hub/bearing assembly.

^ Motor Pack Assembly/Modulator Assembly/Solenoid Valves: The purpose of these components is to modulate brake hydraulic pressure when the antilock brake control module determines wheel lock-up (based on wheel speed sensor inputs). Together with the brake master cylinder, these components make up the brake control assembly.
^ Antilock Brake Control Module: The control module is an electronic device that controls the antilock brake system operation. In addition to the wheel speed sensor input, other inputs to the module include the brake switch, ignition switch, and battery voltage through the ABS enable relay. A serial data link is provided for communication with various diagnostic tools.

BRAKE SYSTEM WARNING LIGHTS
^ Amber ANTILOCK Telltale Lamp: The antilock brake control module continuously monitors itself and other ABS components. If it detects a system problem, the amber ANTILOCK telltale lamp (located in the vehicle instrument cluster) will either flash or light continuously.

The amber ANTILOCK telltale lamp will flash if the problem affects base brake operation.

The amber ANTILOCK telltale lamp will light continuously (solid light) if a problem that will affect the operation of the ABS system is detected. Should this occur, antilock brake control will not be available. Although conventional (non-ABS) brakes will remain operational, repair should be made to the ABS system as soon as possible.

^ Red BRAKE Warning Lamp: Located in instrument cluster, it will light if any of the following conditions are met:
a. Low brake fluid level in master cylinder
b. Parking brake switch is closed
c. It is turned On by the antilock brake control module

IMPORTANT: Certain antilock brake malfunctions may degrade base brake performance. Should this occur, both the amber ANTILOCK and red BRAKE warning lamp will turn On.