This braking system senses any significant difference in wheel speed, from one wheel to another, when a vehicle is braking hard. When any of the wheels begin to lock up (completely stop rotating) while other wheels are rolling, ABS automatically reduces the braking forces to that "locked" wheel or wheels in order to keep all the wheels rolling - to prevent brake-induced skidding.
ABS can control all four wheels (most cars and SUVs have this system) or only two (this is found on some pickup trucks and SUVs). The system can group wheels together in "channels" of operation (i.e. a three-channel system on a four-wheeled vehicle)or have one channel for each wheel. (four-channel ABS).
Four-wheel, four-channel anti-lock braking system (ABS):
The ABS system prevents the vehicle's wheels from locking during hard braking situations and helps drivers maintain the ability to steer the vehicle where they want it to go. The vehicles' automatically engaging loose-surface program helps shorten stopping distances from speeds of less than 18 mph when the transfer case is in low range.