DTC P0440: Evaporative Emission System: Description

WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.

Evaporative Emission (EVAP) system is used to store fuel vapors as to reduce amount of unburned fuel from escaping into the atmosphere. EVAP system consists of EVAP canister, fuel tank pressure sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open), fuel tank and PCM. PCM monitors EVAP system for circuit faults in fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. PCM also monitors EVAP system for large and small leaks. During DTC diagnostic, PCM monitors fuel tank pressure sensor for an atmospheric pressure reading when all DTC parameters have been met with engine running. PCM will then command EVAP vent solenoid on (close valve) and command EVAP purge solenoid to a fixed duty cycle (pulses valve) with engine running. PCM will let pressure drop in fuel tank for a certain length of time after which it will turn off EVAP purge solenoid. DTC sets when a certain vacuum in fuel tank could not be achieved due to a large leak.