In an air brake system, the brake pedal controls which of the following?

• A. The weight of the vehicle
• B. The air pressure applied to put on the brakes
• C. The engine speed
• D. The electrical signals to the brake controller

Answer: (B)

In an air brake system, braking is achieved by applying compressed air to the brake chambers. The brake pedal operates a valve that meters how much air from the reservoirs is sent to the brakes. When you press the pedal, more air pressure reaches the brake chambers, moving the actuators and applying the brakes. Releasing the pedal lets the pressure drop and the brakes release. The pedal doesn’t control the vehicle’s weight or engine speed, and it doesn’t directly send electrical signals to a brake controller in a standard air brake setup—the pedal’s job is to modulate air pressure to apply the brakes.