What should you check to determine if the air filter needs replacement?

To determine if the air filter needs replacement, one should check the air filter restriction gauge. This gauge measures the pressure drop across the air filter and indicates how much the air filter is restricting airflow. When the filter becomes clogged with dust and debris, the restriction gauge will show higher pressure, signaling that the air filter is not allowing air to pass through as efficiently as it should. If the reading on the gauge exceeds a certain threshold, it indicates that the air filter needs to be cleaned or replaced to ensure optimal engine performance and efficiency.

Other options do not directly assess the condition of the air filter itself. Checking the coolant level in the reservoir pertains to the engine’s cooling system, evaluating drive belts for wear focuses on mechanical components essential for vehicle operation, and inspecting wiring for insulation frays relates to electrical safety and functionality. None of these options provide information specific to air filter condition, making the air filter restriction gauge the most important check in this context.