GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H2 🢒 Engine 🢒 Engine Controls and Fuel - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L 🢒 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

Typical Scan Tool Data

FTP Sensor Signal Voltage

Fuel Tank Pressure

1.5 V

Atmospheric Pressure/BARO

Less than 1.5 V

Positive Pressure

More than 1.5 V

Negative Pressure/Vacuum

Circuit/System Description

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path that would cause excess amounts of vacuum to be developed in the EVAP system. With the purge valve open and the canister vent valve open, if the EVAP system vacuum goes above a calibrated threshold, the test will fail.

Conditions for Running the DTC
    • DTCs P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0442, P0443, P0449, P0451, P0452, P0453, P0454, P0464, P0496, P0608, P0609, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138 are not set.
    • The ignition voltage is between 11-18 volts.
    • The barometric pressure (BARO) is more than 74 kPa.
    • The fuel level is between 15-85 percent.
    • The engine coolant temperature (ECT) is less than 35°C (95°F).
    • The intake air temperature (IAT) is between 4-30°C (39-86°F).
    • DTC P0446 runs once per cold start when the above conditions are met.

Conditions for Setting the DTC
    • The fuel tank vacuum is greater than 12 inches H2O vacuum for 5 seconds.
        OR
    • The FTP is less than -2.5 inches H2O or more than +5 inches for 60 seconds after a cold start.

Action Taken When the DTC Sets

DTC P0446 is a Type B DTC.

Conditions for Clearing the MIL/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 canister vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill condition.
    • An EVAP canister filter that is restricted can cause this DTC to set.

Reference Information

Schematic Reference

    •  Evaporative Emissions Hose Routing Diagram
    •  Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Ignition ON and fuel cap removed, verify that the FTP sensor parameter is between 1.3-1.7 volts.
    2. ⇒If not within the specified range, go to the FTP sensor section in Circuit/System Testing.
  2. Install the fuel cap.
  3. 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 11 inches H2O.
    4. ⇒If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: Perform the Circuit/System Verification before proceeding with the Circuit/System Testing.

Restriction

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 11 inches H2O.

⇒If the fuel tank vacuum is greater than the specified value, isolate the restriction by disconnecting one component at a time while the EVAP canister purge solenoid valve is commanded to 100 percent and the vent valve is open.

FTP Sensor

  1. Ignition OFF, disconnect the harness connector at the FTP sensor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal 2 and ground.
    3. ⇒If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the FTP sensor.

Repair Instructions
    •  Evaporative Emission Canister Vent Solenoid Valve Replacement
    •  Evaporative Emission Canister Replacement
    •  Evaporative Emission Hoses/Pipes Replacement - Engine
    •  Evaporative Emission Hose/Pipe Replacement - Chassis
    •  Evaporative Emission System Cleaning
    •  Fuel Tank Pressure Sensor Replacement
    •  Evaporative Emission Hoses/Pipes Replacement - Canister/Fuel Tank
    •  Control Module References for ECM replacement, setup, and programming

Repair Verification

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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 11 inches H2O.