Figure 5.3 5.1.16 – Antilock Braking Systems (ABS) Truck tractors with air brakes built on or after March 1, 1997, and other air brakes vehicles, trucks, buses, trailers, and converter dollies) built on or after March 1, 1998, are required to be equipped with antilock brakes. Many commercial vehicles built before these dates have been voluntarily equipped with ABS. Check the certification label for the date of manufacture to determine if your vehicle is equipped with ABS. ABS is a computerized system that keeps your wheels from locking up during hard brake applications. Vehicles with ABS have yellow malfunction lamps to tell you if something isn’t working. Tractors, trucks, and buses will have yellow ABS malfunction lamps on the instrument panel. Trailers will have yellow ABS malfunction lamps on the left side, either on the front or rear corner. Dollies manufactured on or after March 1, 1998 are required to have a lamp on the left side. On newer vehicles, the malfunction lamp comes on at start-up fora bulb check, and then goes out quickly. On older systems, the lamp could stay on until you are driving over five mph. If the lamp stays on after the bulb check, or goes on once you are underway, you may have lost ABS control atone or more wheels. In the case of towed units manufactured before it was required by the Department of Transportation, it maybe difficult to tell if the unit is equipped with ABS. Look under the vehicle for the electronic control unit (ECU) and wheel speed sensor wires coming from the back of the brakes. ABS is an addition to your normal brakes. It does not decrease or increase your normal braking capability. ABS only activates when wheels are about to lockup. ABS does not necessarily shorten your stopping distance, but it does help you keep the vehicle under control during hard braking.