DTC P0440: EVAP System - Large Leak: Description
WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
The Evaporative (EVAP) emission system large leak test applies vacuum to the EVAP system and monitors the rate of vacuum decay. The control module monitors the Fuel Tank Pressure (FTP) sensor in order to determine the rate of vacuum decay. At an appropriate time, the control module turns the EVAP canister purge valve ON (open) and the EVAP canister vent valve ON (closed). This allows the engine to draw a vacuum on the system. At a calibrated time or vacuum level, the control module turns the purge valve OFF (closed), and tests the system vacuum. If the system is unable to achieve the calibrated vacuum level, the PCM will set DTC P0440.