Antilock Brakes / Traction Control Systems: Description and Operation

The Anti-Lock Brake System maintains vehicle stability and shortens stopping distance during braking by preventing the vehicle's wheels from locking up. The Anti-lock Brake System's primary component operations are outlined below.

Brake Sensors (4)

The Brake Sensors send wheel speed information to the Anti-lock Brake Control Module in the form of AC voltage. The induced AC voltage signal has a frequency proportional to wheel speed.

Pump Motor Speed Sensor

The Anti-lock Brake Control Module uses the Pump Motor Speed Sensor input to check Pump Motor operation. When the pump is operation, voltage is induced into the sensor's coil, and the Anti-lock Brake Control Module monitors this voltage to ensure that the pump motor is working properly.

Anti-lock Brake Control Module

The Anti-lock Brake Control Module controls hydraulic pressure to disc brake calipers by controlling inlet and outlet valve solenoids. Hydraulic pressure is controlled by pulsing the inlet and outlet valves on and off. The Anti-lock Brake Control Module monitors each wheel brake sensor signal to determine wheel lockup. The Anti-lock Brake Control Module also controls the Pump Motor during an ABS stop based on input from the Anti-lock Pedal Travel Switch. The Anti-lock Brake Control Module also monitors all anti-lock brake components and circuitry for faults, and controls the Anti-lock Brakes Indicator.

Solenoid Control Valve Body

The Solenoid Control valve Body contains inlet and outlet valves. The individual components are not serviceable and must be replaced as an assembly. The inlet and outlet valves are controlled by the Anti-lock Brake Control Module.

Anti-lock Brake Fluid Level Switch

The normally closed Anti-lock Brake Fluid Level Switch opens when the hydraulic control unit reservoir fluid level is low. This signals the Anti-lock Brake Control Module to illuminate the ANTI-LOCK Indicator, alerting the driver of a fault in the Anti-lock Brake System.

Anti-lock Brake Pedal Travel Switch

The normally closed Anti-lock Brake Pedal Travel Switch opens when the pedal is depressed approximately 40% down. During ABS braking, the Anti-lock Brake Control Module turns on the Pump Motor. The Anti-lock Brake Control Module turns off the Pump Motor when brake pedal height rises sufficiently to close the Anti-lock Brake Pedal Travel Switch.