ABS Anti-Lock Brakes
Typical ABS Brake System The ABS assembly is made up of a central electronic unit, four solenoid valves and two or more electric hydraulic pumps. The function of the electric hydraulic pump is to supply brake fluid pressure to the braking system by forcing hydraulic pressure to a reservoir located in the accumulator. The four solenoid pressure valves control brake fluid pressure for each individual wheel. During an ABS operation event, one or more of the solenoid valves dump brake line pressure to a particular wheel allowing it to start turning. There are several types of ABS systems; some of the most popular models are based from the Bosch ABS Actuator (BAA), Nippon-Denso ABS Actuator (NAA) systems. The basic design and assembly is the same, the Nippon-Denso system has a separate solenoid relay pack and ABS computer, where as in the Bosch system both the components are combined. Also, there is an immediate connection between the wheel speed sensors and the ECU (engine control unit), these systems are connected by the CAN (Controller Area Network) bus, this system communicates by sending multiple signals to multiple devices at any given time Each wheel has a dedicated wheel speed sensor which sends an electronic signal to the ABS controller, from this signal the rotational speed of the wheel can be determined. The location of wheel speed sensor may vary, on most vehicles the front sensor is made into the steering knuckle, near the front wheel hub or outer CV joint. In the rear of the vehicle the sensor rings are bolted to the rear driver assembly on the ring gear or attached to the outer axle flange on each side. Some even use the vehicles speedometer sensor VSS (vehicle speed sensor) to read rear wheel speed.
Wheel Speed Sensor (configurations may vary)
Common Problems and Fixes