System Diagnosis - EVAP Control

CIRCUIT DESCRIPTION
Applying a vacuum to the EVAP system and monitoring for a vacuum decay checks the evaporative emission system. The Control Module monitors the vacuum level through the fuel tank vacuum sensor signal. At an appropriate time, the EVAP canister purge valve and the [1][2]EVAP vent solenoid turn ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve turns OFF, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a given time period, when all other variables remain constant. A leak, a blockage or a malfunctioning component in the system causes a DTC to set.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.

3. Inspect the service port. Make sure that the dust cap and valve core is not loose or damaged (the valve core may have left hand threads). If the service port is suspect of leakage use the following procedure: Disconnect the purge line from the EVAP Purge solenoid valve.Connect a hand vacuum pump to the service port by placing the hose/adaptor over the unthreaded end portion of the service port. Apply vacuum to 5 in. Hg. If the vacuum does not hold replace the service port (may require line replacement).
4. If the vehicle passes the Service Bay Test then an intermittent leak or restriction had occurred. Check the fuel tank cap for a possible loose or off condition that may have caused this DTC to set.If the Service Bay Test can not be run, proceed to Step 5. If a fault is not currently present the diagnostic table steps will return you to Step 3.
9. Refer to the information supplied with the [1][2]EVAP pressure/purge diagnostic cart on proper setup and adjustment procedures.
10. With pressure applied it may be necessary to disconnect the [1][2]EVAP lines at the components to verify that a line or component is not restricted. A restriction would prevent a vacuum (or the Step 9 test pressure) from forming in the fuel tank.
22. An EVAP Pressure sensor that does not correctly respond to vacuum (or pressure) will cause this DTC to set. The EVAP Pressure Sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).