System Description

The Evaporative Emission (EVAP) System is used to store fuel vapors to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, the fuel tank pressure (FTP) sensor, the EVAP lines and hoses, the EVAP canister purge solenoid valve which is normally closed, the EVAP service port, the EVAP canister vent solenoid valve which is normally open, the fuel tank, and the engine control module (ECM). The ECM monitors the EVAP system for circuit faults in the FTP sensor, the EVAP canister purge solenoid valve and the EVAP canister vent solenoid valve circuits. The ECM also monitors the EVAP system for small and large leaks. During the DTC P0455 diagnostic, the ECM monitors the FTP sensor for an atmospheric pressure reading when all of the DTC parameters have been met with the engine running. The ECM will then command the EVAP canister vent solenoid valve ON which is a closed valve, and command the EVAP canister purge solenoid valve to a fixed duty cycle. The ECM will let the pressure drop in the fuel tank for a certain length of time after which it will turn OFF the EVAP canister purge solenoid valve. DTC P0455 sets when a certain vacuum in the fuel tank could not be achieved due to a large leak or a lack of vacuum source.