DTC P0446: Evaporative Emissions (EVAP) Vent System Performance
Circuit/System Description
This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid valve Open and the EVAP canister vent solenoid valve Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inch H2O in a calibrated time, this DTC sets.
Diagnostic Aids
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An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP canister vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.
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An EVAP canister, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using a purge solenoid command with a scan tool will allow vacuum to be applied to the system instead of pressure. With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than 5 inches H2O.
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An EVAP canister filter that is restricted can cause this DTC to set. Refer to Evaporative Emission Canister Replacement .
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Disconnecting one component at a time while the EVAP system is under flow will help to pinpoint a restriction in the system
Do you have a scan tool that reads data PID'S ?
Your FTP - fuel tank pressure sensor could be at fault !
Ignition ON and fuel cap removed, verify that the FTP sensor parameter is between 1.3-1.7 volts.
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If not within the specified range, go to the FTP sensor section in Circuit/System Testing.
- Install the fuel cap.
- With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than 12 inches H2O.
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If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.
If
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