DTC P0446: EVAP Vent System Performance: Description

This DTC tests Evaporative (EVAP) emission system for a restricted or blocked EVAP vent path. Powertrain Control Module (PCM) commands EVAP canister purge valve on and EVAP canister vent valve on. This allows a vacuum to be applied to EVAP system. Once a calibrated vacuum level has been reached, PCM commands EVAP canister purge valve off and EVAP canister vent valve off. PCM monitors Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. DTC sets when vacuum does not decrease to about zero in. H2O in a calibrated time.

For 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 LOGIC  table under DTC P0440: EVAP SYSTEM.