DTC P0440: EVAP System: Description

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Powertrain Control Module (PCM) tests Evaporative (EVAP) emission system for a large leak. PCM monitors Fuel Tank Pressure (FTP) sensor signal to determine EVAP system vacuum level. When conditions for running are met, PCM commands EVAP canister purge valve open and EVAP vent valve closed. This allows engine vacuum to enter EVAP system. At a calibrated time, or vacuum level, PCM commands EVAP canister purge valve closed, sealing system, and monitors FTP sensor input to determine EVAP system vacuum level. DTC sets when system is unable to achieve calibrated vacuum level, or vacuum level decreases too rapidly.

The EVAP VALVE LOGIC table illustrates the relationship between the on and off states, and the open or closed states of the EVAP canister purge and vent valves.

EVAP VALVE LOGIC

PCM Command	EVAP Purge Valve	EVAP Vent Valve
On	Open	Closed
Off	Closed	Open