Exhaust brakes operate by doing what?

• A. Restricting fuel supply
• B. Blocking the ignition
• C. Restricting exhaust flow to create back pressure
• D. Applying drum brakes

Answer: (C)

Exhaust brakes work by partially closing a valve in the exhaust system, restricting exhaust flow to create back pressure. That back pressure makes the engine resist the motion of the vehicle, turning the engine into a brake itself and slowing you down without using the wheel brakes. It does not operate by cutting fuel supply, nor by blocking the ignition, nor by applying the wheel brakes. This is a common technique on diesel-powered emergency vehicles to help control speed on descents or during towing.