GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0446

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0446: Evaporative Emissions (EVAP) Vent System Performance

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 11-18 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 greater 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 greater than 16 minutes or the long term fuel trim is stable.
    • The conditions above exist for greater than 5 seconds.
    •  DTC P0446 will attempt to run up to 10 times or until 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 condition is present for greater than 4 seconds or a cumulative of 50 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

Component Connector End Views

Description and Operation

Evaporative Emission Control System Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • 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
    • CH-48096 EVAP Service Port Access Tool
    • GE-41415-50 Fuel Tank Cap Adapter

Circuit/System Testing
  1. Verify DTCs P0458, P0459, P0498, P0499, P0452, or P0453 are not set.
    2. ⇒If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  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 DTC P0452 or P0453 .
  4. Reconnect 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. Ignition ON, seal the EVAP system with a scan tool.
  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 H2O.
  9. While observing the FTP sensor parameter with a scan tool, command the EVAP vent valve OFF. Verify the FTP Sensor parameter is 0 inches H2O.
    10. ⇒If not at the specified value, test for a blockage or a restriction in the EVAP vent hose, or replace the EVAP vent solenoid valve.
  10. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Repair Instructions

Evaporative Emission Hoses/Pipes Replacement - Chassis/Canister

Repair Verification
  1. Ignition ON, seal the EVAP system with a scan tool.
  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 inches H2O.
  4. While observing the FTP sensor parameter with a scan tool, command the EVAP vent valve OFF.
  5. Verify the FTP Sensor parameter is 0 inches H2O.