The engine brake and retarder are activated when

• A. Accelerator is fully depressed
• B. Pressure is released from the accelerator
• C. Parking brake engaged
• D. Vehicle reaches idle speed

Answer: (B)

Engines brakes and retarders slow the vehicle by creating resistance in the engine when you ease off the throttle. The moment you release the accelerator, the throttle closes, causing the engine to work against the drivetrain. This resistance—often enhanced by backpressure in the exhaust brake or by the retarder mechanism—transforms kinetic energy into heat, providing deceleration without using the service brakes. If you push the pedal further down, the engine is delivering more power and the braking effect decreases. The parking brake is a separate device used to hold the vehicle in place, not to provide the continuous deceleration of engine braking. Idle speed is simply the engine’s low RPM state, not an active braking condition.