Engine brake activation occurs when the accelerator is

• A. Pressed
• B. Released from the accelerator
• C. Engaged with the park brake
• D. Idling at a stop

Answer: (B)

Engine braking is activated when you lift off the accelerator. When the pedal is released, the throttle closes and the engine works against the moving vehicle, creating pumping losses that convert some of the kinetic energy into heat and slow the truck. If an engine brake (like a Jake brake) is engaged, that braking action is enhanced by the engine’s exhaust process, but the core idea is that no longer pressing the accelerator allows the engine to resist the motion.

Pushing the accelerator increases fuel and power, which reduces braking. The park brake is a separate system and not engine braking. Idling at a stop doesn’t provide braking because the vehicle isn’t moving and the engine’s braking effect isn’t being used to slow a load.