Large Leak Test
WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
This tests for large leaks and blockages in the EVAP system. The Powertrain Control Module (PCM) will command the EVAP vent valve ON, closed, and command the EVAP purge valve ON, open, with the engine running, allowing engine vacuum into the EVAP system. The PCM monitors the Fuel Tank Pressure (FTP) sensor to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. The PCM then commands the EVAP purge valve OFF, closed, sealing the system and monitors the vacuum level for decay. If the PCM does not detect that the predetermined vacuum level was achieved, or the vacuum decay is more than a calibrated level on 2 consecutive tests, a DTC P0440 will set.