Circuit Description

This DTC tests EVAP system for a restricted or blocked EVAP vent path. 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. If vacuum does not decrease to near zero inches H2O in a calibrated time, this DTC P0446 will set.