C. Inspect the "Fresh Air" Circuit

1. Visually inspect the two way valve to ensure the arrow points toward the canister close valve (fresh air).

2. Inspect the plastic tube located inside the frame rail of the vehicle for the presence of moisture or foreign material.

3. Remove the canister close valve and blow through it in both directions. The valve should allow air to pass through it without it being energized. Energize the valve with 12 volts, and then try to blow through it in both directions. The valve should not allow air to pass through it when energized. While blowing through the valve, release the 12 volts to determine if the valve opens immediately or sticks closed. Replace the valve if it sticks closed.

4. Disconnect the vapor hose from the "Purge" port on the canister.

5. Install the "test" hose on the "Purge" port of the canister.

6. Apply hose pinching pliers to the hose located between the canister close valve and the air filter.

7. Place HDS in the "DIGITAL RECORD" mode. While watching the DPS signal on HDS, GENTLY begin to blow into the "test" hose (the DPS voltage should begin to rise). Continue to gently blow into the hose until the DPS voltage is approximately 4.0 volts. Do not over-pressurize since the sensor cannot read over 4.5 volts.

8. Apply hose pinching pliers on the "test" hose. The DPS should read a constant value at this point (if the value does not remain constant +/- 0.05 volts over 10 seconds refer to "P0455/P0442 Leaks" section and then return to finish this inspection).

9. Disconnect the hose from the "Fresh Air" port of the canister. The system should return to atmospheric pressure in approximately 45 seconds. If it takes longer than 45 seconds, inspect the "Fresh Air" circuit for restricted vapor hoses or internal blockages. If the system returns to atmospheric pressure within 45 seconds, repeat entire procedure verifying each step.

10. Use the "Pressurize/Clamp/Observe" method to isolate the blockage by disconnecting different points, each time farther from the canister in the "Fresh Air" circuit.