What is the primary function of a compression brake rocker arm?

The primary function of a compression brake rocker arm is to actuate exhaust valves. In a compression braking system, the rocker arm plays a crucial role in controlling the opening and closing of the exhaust valves during the engine's operation. By doing so, it allows the engine to use the compression forces generated during the engine cycle to slow down the vehicle. When the exhaust valves are opened at the right moment, the air that is compressed within the cylinder is released, which creates resistance against the motion of the vehicle, effectively slowing it down. This is particularly useful for heavy vehicles that require additional braking power when descending steep grades.

The other options, while possibly relevant to engine operation in a broader context, do not accurately describe the function of the compression brake rocker arm. Enhancing fuel efficiency or improving throttle response typically involves different components and mechanisms in the engine system. Additionally, cooling the engine is primarily managed by the cooling system and not directly related to the operation of the rocker arm. Thus, the correct answer emphasizes the specific function that directly contributes to the mechanics of compression braking.