Service function guideVacuum Leak Diagnosis

This service function guide teaches you how to find vacuum leaks by combining fuel trim analysis with smoke testing, a method that works on any gasoline engine with a manifold absolute pressure sensor or mass airflow sensor. You will learn how the intake system seals, why unmetered air corrupts the air-fuel ratio, and how to read positive fuel trims as a diagnostic clue before you ever open a smoke machine. The procedure covers preparation, safe smoke injection, interpretation of results, and verification with a scan tool, with variations for naturally aspirated, turbocharged, and direct-injection engines. After finishing, you will be able to isolate a leaking intake gasket, cracked hose, or faulty purge valve in under an hour and confirm the repair with a fuel trim test drive.