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ABS Brake System Types

Antilock brake systems operate basically the same way but with different configurations. The wheel speed sensor sends a signal to the ABS controller and the controller compares this data to the preset data stored in the systems memory. The controller then sends signals to actuator valves located in the hydraulic brake actuator to hold, increase, or decrease pressure to the desired brake circuit.

ABS systems are classified by channels, whether they are two-wheel or four-wheel, and the level of control they provide. The simplest type is the one- channel two-wheel system. This system uses one speed sensor usually located on the axle housing and both rear brakes are controlled by the same hydraulic circuit at the same time.

A two-channel two-wheel system has a speed sensor dedicated to each rear wheel located on each side of the axle tube. It also has individual hydraulic circuits dedicated to each of the rear wheels.

A three-channel four-wheel system is often found on light trucks and SUV's. This system uses three 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 steering control during hard braking situations.

The diagonal-split systems found on many front wheel drive vehicles use two wheel speed sensors to control four wheels. The sensors are located on the front wheels and the left front circuit shares the same modulation as the right rear. The right front sensor shares the same hydraulic control or modulation as the left rear. That's why they call it the diagonal-split system. An obvious advantage of this system is that it provides steering control as well.

The best type of ABS system is a four-channel four-wheel system. This system has a speed sensor and hydraulic circuit dedicated to each wheel. This system assures the driver that each wheel is controlled by the module preventing a skid situation. This can be important because in a three-channel system it is possible that one of the rear wheels may skid loosing traction.