Description & Operation
Anti-Lock Brake System (ABS) consists of hydraulic unit, actuator, solenoids, pump motor, ABS Electronic Control Unit (ECU), relays and wheel speed sensors. See Fig 1. ABS warning light, BRAKE warning light, VSC warning light, and TRAC OFF indicator light are located in instrument cluster. ABS ECU performs a bulb test by illuminating ABS warning light, BRAKE warning light, VSC warning light, and TRAC OFF indicator light for 3 seconds when ignition is turned on. A primary check is performed after each engine start, and when initial vehicle speed exceeds 6 MPH. Under normal operation, an actuator noise is heard as vehicle is started or as speed exceeds 6 MPH. Anti-lock system remains active until vehicle speed drops to less than 3 MPH.
When parking brake is applied or the level of brake fluid is low, BRAKE warning light illuminates. Under normal driving conditions, ABS functions as a standard brake system. With detection of wheel lock-up, short pedal pulsations occurring in rapid succession will be felt in brake pedal. Pedal pulsation will continue until there is no longer a need for ABS function, or until vehicle speed falls to less than 3 MPH. Maintaining constant force on brake pedal provides shortest stopping distance.
The EBD (Electronic Brake force Distribution) system distributes optimal breaking force to the front and rear tires in accordance with driving conditions. Furthermore, braking force is distributed to the left and right wheels during braking when cornering to ensure vehicle performance and superior braking power.
Vehicles are also equipped with traction control (TRAC) and Vehicle Skid Control (VSC) systems. When a failure occurs in the ABS & BA & TRAC & VSC systems, the ABS warning light, the VSC warning light and the TRAC OFF indicator light turns on and the ABS & BA & TRAC & VSC operations are prohibited. In addition, when there is a failure that disables the EBD operation, the brake warning light also turns on and the EBD operation is prohibited. For component locations, see Fig 1.
The anti-lock brake system is equipped with a self-diagnostic capability which allows technician to retrieve data stored in control module to aid in diagnosis. See SELF-DIAGNOSTIC SYSTEM .