Which of the following describes the action of the engine brake and retarder?

• A. They are activated when pressure is released from the accelerator
• B. They are activated when you press the accelerator
• C. They replace the service brakes
• D. They are the same as the parking brake

Answer: (B)

Engine brake and retarder slow the vehicle by converting some of the engine’s or drivetrain’s energy into braking force, without relying on the service brakes. They’re engaged when you reduce throttle input (ease off the accelerator) and, for the retarder, when you activate its control. This lets you control speed—especially on downgrades—and reduces wear and heat on the service brakes. They don’t replace the service brakes, and they’re not the parking brake. Pressing the accelerator does the opposite of braking, so activation is not tied to pressing the throttle.