Intake Air Bypass Control Thermal Valve Test

Special Tools Required 

Vacuum pump/gauge, 0-30 in.Hg, Snap-on YA4000A or equivalent, commercially available

1. Start the engine, and let it idle.
   NOTE: Engine coolant temperature must be below 149 °F(65 °C).
2. Remove the vacuum hose (A) from the intake air duct, and connect the vacuum pump/gauge, 0-30 in.Hg, to the hose.
   Fig 1: Removing Vacuum Hose From Intake Air Duct And Connecting Vacuum Pump/Gauge

   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 damage intake air bypass control thermal valve.
4. Hold the engine speed at 3,000 RPM without 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 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.