DTC P0440: Evaporative Emission System: Description

The Evaporative Emission (EVAP) large leak test applies vacuum to EVAP system and monitors vacuum decay. PCM monitors Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, PCM turns the EVAP canister purge valve and vent valve are turned on. This allows engine to draw a vacuum on EVAP system. At a calibrated time or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the VTP sensor input in order to determine EVAP system vacuum. DTC will set if system is unable to achieve the calibrated vacuum level or vacuum level decreases too rapidly.