ABS Brake System: Channels

Wheel speed sensor function.

Channels classify ABS systems. The simplest system is the one-channel two-wheel system that has one circuit that controls hydraulic pressure to both rear wheels. This system uses one speed sensor that is bolted to the axle housing. This lone sensor inputs a signal for control of both the left and the right rear hydraulic brake circuits. A two-channel, two-wheel system has a wheel speed sensor and hydraulic circuit dedicated to each rear brake circuit.

The three-channel, four-wheel system found on many light trucks and SUV's uses three wheel speed sensors, one for each of the front wheels and a single sensor for the rears. The rear brakes also share a hydraulic control circuit for both sides.

The most efficient ABS brake system is the four-channel, four-wheel system. This system has a speed sensor and hydraulic circuit dedicated to each wheel. The module controls each wheel during a skid situation. This type of system offers skid and improved steering control during hard braking situations.

Different manufacturers use different names and configurations to provide skid control. A wheel speed sensor sends a signal to the ABS controller, and the controller compares this data to the preset data and parameters stored in its memory. The controller then sends a signal to an actuator valve located in the hydraulic brake actuator to hold, decrease or increase pressure to the desired brake circuit.

The diagonal-split systems found on older front-wheel-drive vehicles use two wheel speed sensors to control four wheels. The left front circuit shares the same modulation as the right rear. The right front wheel speed sensor shares the same hydraulic control or modulation as the left rear. A distinct advantage of this system is that it provides steering control as well as skid control.