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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 LaCrosse 🢒 Restraints 🢒 SIR 🢒 DTC P0446

DTC Descriptor

DTC P0446: Evaporative Emissions (EVAP) Vent System Performance

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Description

A restricted or blocked evaporative emission (EVAP) vent path is detected by the control module commanding the purge valve ON (open) and the vent valve ON (closed) allowing a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the purge valve OFF (closed) and the vent valve OFF (open) while monitoring the fuel tank pressure (FTP) sensor for a decrease in vacuum.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves.

Control Module Command

EVAP Canister Purge Valve

EVAP Canister Vent Valve

ON

Open

Closed

OFF

Closed

Open

Conditions for Running the DTC
    • Before the engine control module (ECM) can report DTC P0446 failed, DTC P0452 and P0453 must run and pass.
    • DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0221, P0222, P0223, P0443, P0449, P0451, P0452, P0453, P0458, P0459, P0496, P0498, P0499, P0560, P0562, P0563, P0700, P2122, P2123, P2127, P2128, and P2138, are not set.
    • The ignition 1 voltage is between 10.5-18 volts.
    • The fuel system is operating in closed loop.
    • The engine is idling.
    • The ambient air temperature is between 2-32°C (36-90°F).
    • The start-up engine coolant temperature (ECT) is within 10°C (18°F) of ambient air temperature.
    • The FTP is between -1.8 to +7.5 mm Hg (-1.0 to +4.0 in H2O).
    • The volumetric efficiency is less than 35 percent.
    • The barometric pressure (BARO) is more than 68 kPa.
    • The fuel level is between 12-88 percent.
    • The vehicle speed sensor (VSS) is less than 2 km/h (3 mph).
    • The engine is operating for more than 16 minutes or the long term fuel trim is stable.
    • The conditions above exist for more than 5 seconds.
    • DTC P0446 will attempt to run up to 10 times or the test completes successfully once per ignition cycle.

Conditions for Setting the DTC
    • The FTP is less than -2.0 mm Hg (-1 in H2O).
    • The ECM detects a large leak in the EVAP system.
    • The condition is present for more than 4 seconds.

Action Taken When the DTC Sets

DTC P0446 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0446 is a Type B DTC.

Diagnostic Aids

An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Special Tools Required

    • J 41413-SPT High Intensity White Light
    • J 41413-VLV EVAP Port Vent Fitting Tool
    • J 41413-200 Evaporative Emissions System Tester (EEST)
    • J 41413-300 EVAP Cap and Plug Kit
    • GE-41415-50 Fuel Tank Cap Adapter

Circuit/System Testing
  1. Inspect the evaporative emission (EVAP) system for the following conditions: · A damaged EVAP vent valve · A collapsed or restricted EVAP vent hose/pipe (if equipped) ·
    2. • A damaged EVAP vent valve
    •  A collapsed or restricted EVAP vent hose/pipe (if equipped)
    •  A damaged EVAP canister
    ⇒If you find any of the above conditions, repair as necessary.
  2. Disconnect the purge line from the EVAP purge valve.
  3. Ignition ON, observe the fuel tank pressure sensor parameter with a scan tool. The FTP sensor parameter should be 0 inches H2O. If the pressure is not at 0 inches H2O, verify the FTP sensor voltage is less than 4.7 volts.
    4. ⇒If the FTP sensor voltage is greater than 4.7 volts, refer to Fuel Tank Pressure Sensor Replacement .
  4. Connect all previously disconnected EVAP hardware.

    5. Important: Refer to the J 41413-200 Evaporative Emissions System Tester (EEST) operation manual for detailed instructions.

  5. Remove the fuel fill cap and connect the GE-41415-50 to the fuel tank filler neck. Connect the J 41413-200 to the GE-41415-50 .
  6. Disconnect the EVAP vent line from the vent solenoid, and seal it, using a suitable plug or a plug from the J 41413-300 .
  7. Turn the nitrogen/smoke valve on the J 41413-200 to nitrogen.

    8. Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  8. Use the remote switch to activate the J 41413-200 and pressurize the fuel tank with nitrogen to 5 inches H20.
  9. While observing the FTP sensor parameter with a scan tool, remove the EVAP vent valve plug. Verify the FTP Sensor parameter is 0 inches H2O.
    10. ⇒If the FTP is not at the specified range , test for a blockage or a restriction in the EVAP vent hose.
  10. If all hoses/pipes test OK, replace the EVAP vent solenoid valve

Repair Instructions
    •  Evaporative Emission Canister Vent Solenoid Valve Replacement
    •  Fuel Tank Pressure Sensor Replacement
    •  Evaporative Emission Canister Replacement

Repair Verification
  1. Disconnect the EVAP vent line from the vent solenoid, and seal it, using a suitable plug or a plug from the J 41413-300 .
  2. Turn the nitrogen/smoke valve on the J 41413-200 to nitrogen.

    3. Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  3. Use the remote switch to activate the J 41413-200 and pressurize the fuel tank with nitrogen to 5 in H20.
  4. While observing the FTP sensor parameter with a scan tool, remove the EVAP vent valve plug.
  5. Verify the FTP Sensor parameter is 0 in H2O.