DTC P0446: EVAP Emission Control System Vent Control Circuit: Description

This DTC tests the Evaporative (EVAP) emission system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge valve ON and the EVAP canister vent valve ON. This allows a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge valve OFF and the EVAP canister vent valve OFF. The control module monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to about 0 in. H2O in a calibrated time, this DTC sets. The EVAP valve command table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves. See EVAP VALVE COMMAND  table under DTC P0440: EVAP SYSTEM - LARGE LEAK.