Illinois CDL Practice Exam

What does the Trailer Air Supply Control allow a driver to do?

1. Adjust the trailer weight distribution

2. Control the trailer suspension stiffness

3. Engage the trailer brakes automatically during turns

4. Supply air to the trailer or activate emergency brakes

The correct answer is: Supply air to the trailer or activate emergency brakes

The Trailer Air Supply Control is a crucial component in a commercial vehicle's braking system, specifically designed to manage how the trailer receives air supply from the tractor's air system. The primary function of this control is to provide the necessary air pressure that allows the trailer's service brakes to operate effectively. When the driver activates the Trailer Air Supply Control, it not only supplies air to the trailer brakes but also can engage the trailer's emergency brakes if needed. This is particularly important in the event of an emergency situation where the trailer needs to stop quickly, or if there is a loss of air pressure. The ability to supply air to the trailer ensures that the vehicle maintains safe and effective braking performance, particularly in combination with the tractor. Other functions such as adjusting trailer weight distribution, controlling suspension stiffness, or engaging brakes during turns, do not fall under the responsibility of the Trailer Air Supply Control. Instead, those tasks are managed by different systems or controls within the vehicle, making the primary focus of this control vital for maintaining safety and responsiveness while driving a commercial vehicle.