Intake Air Bypass Control Thermal Valve Test

Special Tools Required:  Vacuum Pump/Gauge, 0-30 in. Hg A973X-041-XXXXX

1. Start the engine, and let it idle.
   NOTE: The engine coolant temperature must be below 104°F (40°C).
2. Remove the vacuum hose (A) from the intake duct and connect a vacuum gauge to the hose.
   Fig 1: Removing The Vacuum Hose From The Intake Duct & Connecting A Vacuum Gauge To The Hose

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
3. Raise and lower the engine speed, and make sure the vacuum gauge reading changes as the rpm changes.

   If the vacuum reading changes, go to step 4.

   If the vacuum reading does not change, check for these problems:

   • Misrouted, leaking, broken, or clogged intake air bypass system vacuum lines.
   • A cracked or defective intake air bypass control thermal valve.
4. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
5. Raise and lower the engine speed, and make sure the vacuum gauge reading does not change as the rpm changes.

   If the vacuum reading does not change, the intake air bypass control thermal valve is OK.

   If the vacuum reading changes, check for these problems:

   • Misrouted, leaking, broken, or clogged intake air bypass system vacuum lines.
   • A cracked or defective intake air bypass control thermal valve.