Antilock brake systems (ABS) are a vehicle safety mechanism that mechanically pumps the brakes so that they don't lock up. This gives a driver the ability to focus more on steering the vehicle instead of having to manually pump the brakes to prevent lockup. This can be a huge advantage in an emergency situation, such as driving on a road that's wet or is covered with ice.
Four-Wheel Antilock Brakes
A four-wheel antilock braking system is found on most cars and minivans. The primary purpose of this type of ABS system is to prevent the brakes from locking up on any of the vehicle's four wheels. The system sensors ensure that each wheel has the necessary force to brake to help the driver maintain control of his steering.
Rear-Wheel Antilock Brakes
In contrast to the four-wheel system, this type of ABS helps to keep the rear wheels only on a vehicle from spinning out beyond the driver's control. The brakes on the front wheels can still become locked, which can give the driver less control over the vehicle's steering. This type of system is found primarily on many trucks, sport-utility vehicles and some models of vans. This setup is essential when the driver is towing a light load behind the vehicle.
Three-Channel Antilock Brake System
This type of ABS has the control divided between the front and the rear wheels. Both front wheels have an independent control system, while the rear wheels have an ABS that's controlled by a single circuit between the two of them. The electronic control module, or ECM, senses when the rear wheels may lock up and signals the system to apply the necessary power to prevent it. It also does continual diagnostics on the system while controlling it.
