EVAP Purge/Seal Function

NOTE: Ensure vehicle underbody temperature is similar to ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. Fuel tank pressure may increase on a hot vehicle due to thermal expansion of vapors in fuel tank. Fuel tank fill levels can affect the results of the diagnostic procedure. Fuel tank pressure may increase on a warm vehicle that has less than one third a tank of fuel.

EVAP purge/seal function is designed to seal the EVAP system with a vacuum applied. The test allows the technician to monitor Fuel Tank Pressure (FTP) sensor, for any vacuum decay. The purge/seal function can also alert the technician of an inoperable purge, vent, or pressure switching solenoid. When the EVAP purge/seal function is enabled, PCM commands vent and pressure switching solenoids ON (closed). The purge solenoid is commanded ON (open) allowing a vacuum to enter EVAP system. After 30 seconds, PCM commands purge solenoid OFF (closed), sealing the system. EVAP system will remain sealed for 150 seconds. FTP sensor reading should be approximately -12.50 in. H2O. To perform EVAP purge/seal test with the scan tool follow the procedures below:

Run engine to normal operating conditions.
Install scan tool.
Turn ignition switch to RUN position, engine OFF.
Remove fuel fill cap. FTP sensor should read near 0.0 in. H2O.
Install fuel fill cap and start the engine.
Enable EVAP purge/seal function on the scan tool.
FTP sensor reading should decrease to a -12.50 in. H2O, indicating a vacuum has entered the system.
Observe FTP sensor reading for 2 minutes. If there is no evidence of vacuum decay, FTP sensor reading should remain at -12.50 in. H2O.