ABS Brake System: Channels
All Anti-Lock Brake systems operate basically the same way. Different manufacturer's use different names and configurations to provide the same thing, 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.
ABS systems are classified by channels, depending on how many hydraulic circuits control each wheel. The simplest system is the one-channel two-wheel system. It has one circuit that controls hydraulic pressure to both rear wheels. This system uses one speed sensor, usually located on the axle housing. This lone sensor inputs a signal for control of both the left and the right rear brake hydraulic 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 is often found on light trucks and SUV's. These systems use three wheel speed sensors, one for each of the front wheels and a common sensor for the rears. The rear brakes also share a common hydraulic control circuit for both sides. This type of system offers skid and improved steering control during hard braking situations.
The diagonal-split systems found on many front wheel drive vehicle's use two wheel speed sensors to control four wheels. The sensors are located on the front 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. That's why they call it a diagonal-split system. An obvious advantage of this system is that it provides steering control as well.
The most efficient ABS system is a four-channel, four-wheel system. This system has a speed sensor and hydraulic circuit dedicated to each wheel. Each wheel is controlled by the module while preventing a skid situation. This can be important because even in a three-channel system it is possible that one of the rear wheels may skid loosing traction.