most often its the purge or vent solenoid but i will supply the flow chart for diagnostic procedures
Circuit Description The Evaporative System includes the following components:
The Evaporative Leak Detection Diagnostic Strategy is based on applying a vacuum to the EVAP system and monitoring the vacuum decay rate. The VCM monitors the vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid turn ON, allowing the engine vacuum to draw a small vacuum on the entire evaporative emission system. If a sufficient vacuum level cannot be achieved, a large leak or a malfunctioning EVAP purge solenoid is indicated. The following conditions can cause this problem:
Any of the above conditions can set a DTC P0440.Conditions for Running the DTC
Conditions for Setting the DTC The EVAP system is unable to generate a vacuum greater than a calibrated value over a specified period of time.Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
Diagnostic Aids Important: An accurate indication of fuel level is required for the VCM to properly pass or fail this DTC. Always diagnose fuel level sensor DTCs before performing this DTCs diagnostic table. Always check for fuel level sensor DTCs stored in history.Check for the following conditions:
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.Test Description Number(s) below refer to the step number(s) on the Diagnostic Table.