Intake Air Bypass Control Thermal Valve Test

Special Tools Required 

Vacuum pump/gauge 0-30 in.Hg A973X-041-XXXXX

1. Start the engine. Then let it idle.
   NOTE: The engine coolant temperature must be below 149°F (65°C).
2. Remove the vacuum hose (A) from the intake air duct, and connect a vacuum pump/gauge to the hose.
   Fig 1: Connecting A Vacuum Pump/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 engine speed changes.

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

   • Misrouted, leaking, broken, or clogged intake air bypass control system vacuum lines.
   • A cracked or damaged intake air bypass control thermal valve.
4. Hold the engine at 3,000 rpm with no load (in 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 changes, check for these problems:

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