HET Truck and Transport Mechanic Practice Exam

The purpose of the air filter in a truck is fundamentally to prevent dirt and debris from entering the engine. An internal combustion engine requires a precise mixture of air and fuel for optimal performance, and the air filter plays a crucial role in ensuring that the air entering the engine is clean and free of contaminants. When air flows through the filter, it traps particulate matter, such as dust, pollen, and other impurities, which could cause damage to sensitive engine components if left unfiltered. Protecting the engine from these particles helps maintain efficiency, prolongs the engine's lifespan, and ensures reliable performance.

While improving fuel efficiency can be a secondary benefit of having a clean air filter, the primary function is to safeguard the engine from harmful substances. The other options do not accurately represent the primary role of the air filter; enhancing sound and cooling the engine are not related to the function of air filtration. Therefore, the correct answer captures the essential duty of the air filter in maintaining engine health.