System Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

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 P0446 diagnostic, the EVAP canister purge solenoid valve is commanded to a fixed duty cycle, and the EVAP canister vent solenoid valve is commanded ON, closed, in order to build vacuum. Once vacuum is obtained, the EVAP canister vent solenoid valve is commanded OFF, open, and the vacuum should decrease rapidly. DTC P0446 sets when the vacuum decay is too slow, indicating a blocked vent system.