Meritor WABCO® Antilock Braking System (ABS), Hydraulic Brake Systems
Warning: Although the ABS improves vehicle control during emergency braking situations, the driver still has the responsibility to change driving styles depending on existing traffic and road conditions. Failure to change driving styles to accommodate existing traffic and road conditions could cause an accident, possibly resulting in personal injury or death, or property damage.
The Meritor WABCO Antilock Braking System (ABS) is an electronic wheel speed monitoring and control system that works with the hydraulic brake system. ABS passively monitors vehicle wheel speed at all times, but controls wheel speed during an emergency or reduced-traction stop. In normal braking applications, the standard hydraulic brake system is in effect.
Important: For proper ABS operation, do not mismatch tire sizes among any of the tires on the vehicle. Mismatching tire sizes could result in a reduced braking force, leading to longer stopping distances and cause an ABS event to register on the electronic control unit (ECU).
Warning: An accumulation of road salt, dirt, and debris on the ABS tone wheels and sensors can cause the ABS warning light to illuminate. If the ABS light illuminates while driving, have the ABS serviced. Operating the vehicle when the ABS needs to be serviced could cause an accident, possibly resulting in personal injury or death, or property damage.
Important: During winter months in areas where corrosive materials are used on the highways, periodically clean the underside of the vehicle to ensure proper ABS functioning. The required frequency of cleaning will vary with conditions. In general, do not allow corrosive materials to remain on the underside of the vehicle for extended periods of time.
The electronic control unit monitors the wheel sensors, solenoid control valves, and the electrical circuitry. The ABS warning light illuminates after turning the ignition switch to the ON position. The warning light goes out only if all of the vehicle's ABS components are working properly.
The Meritor WABCO ABS combines one front-axle control channel with the rear axle (four sensor system) to form one control circuit. For example, the sensor and solenoid control valve at the left-front axle form a control circuit with the sensor and solenoid valve on the right-rear axle. If, during vehicle operation, the safety circuit senses a failure in any part of the ABS (a sensor, solenoid control valve, wiring connections, short circuit, etc.), the ABS warning light illuminates and the control circuit where the failure occurred is switched to normal braking action. The remaining control circuit will retain the ABS effect. Even if the ABS is partially or completely inoperative, normal braking ability is maintained . An exception would be if a solenoid control valve (or combination solenoid control valve) is damaged and inoperative. As these components are an integral part of the air brake system, normal braking may be impaired or inoperative.
Warning: If any of the ABS warning lights do not work as described above or illuminates while driving, repair the ABS immediately to ensure full antilock braking capability. Operating the vehicle when the ABS needs to be serviced could cause an accident, possibly resulting in personal injury or death, or property damage.
During emergency or reduced-traction stops, fully depress the brake pedal until the vehicle comes to a safe stop; do not pump the brake pedal. With the brake pedal fully depressed, the ABS will control all wheels to provide steering control and a reduced braking distance.
Operation
Before driving the vehicle, secure all loose items in the vehicle so that they will not fly forward during a full brake application. Check that the brake system warning light is off after releasing the parking brake. If the warning light does not go off, correct the problem before continuing operation of the vehicle.
During normal brake stops, depress the foot brake control pedal until braking action slows down the vehicle. Increase or decrease the pressure on the pedal so that the vehicle comes to a smooth, safe stop. When the vehicle comes to a complete stop, shift the transmission into park (P) on the shifter and apply the parking brake.
Notice: If the vehicle is equipped with an air suspension system, do not park the vehicle or move the vehicle with the air suspension deflated. This may cause suspension component damage.