GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 Terraza Ext. 🢒 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

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The engine control module (ECM) 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 ECM commands the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Open. The ECM monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. The vacuum should decrease to near 0 inch H2O in the calibrated period of time.

FTP Sensor Signal Voltage

Fuel Tank Pressure

Less than 1.5 V

Positive Pressure

More than 1.5 V

Negative Pressure/Vacuum

Conditions for Running the DTC
    • DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0125, P0128, P0502, P1106, P1107, P1111, P1112, P1114, P1115, P1125, P1516, P2101, P2108, P2119, P2120, P2125, P2138 are not set.
    • The ignition voltage is between 10-18 volts.
    • The barometric pressure (BARO) is more than 75 kPa.
    • The fuel level is between 15-85 percent.
    • The start-up engine coolant temperature (ECT) is between 4-30°C (39-86°F).
    • The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
    • The start-up ECT and IAT are within 9°C (16°F) of each other.
    • The vehicle speed sensor (VSS) is less than 129 km/h (80 mph).
    • DTC P0446 runs once per trip when the above conditions have been met.

Conditions for Setting the DTC

The FTP sensor is more than 8 inches H2O vacuum for 2 seconds during the 13 minute test.

OR

The FTP is less than -2.5 inches H2O or more than +5 inches H2O for 3 seconds after a cold start ignition ON.

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 problem.
    • 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.
    • An EVAP canister filter that is restricted can cause this DTC to set. Refer to Evaporative Emission Canister Replacement.
    • Disconnecting one component at a time while the EVAP canister purge solenoid valve is commanded to 100 percent and the vent valve is open will help to pinpoint a restriction in the system.

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 the FTP sensor parameter is between 1.3-1.7 volts.
    2. ⇒If greater than the specified range, refer 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 8 inches H2O.
    4. ⇒If greater than the specified range, refer to the restriction section in Circuit/System Testing.

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 8 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
    •  Fuel Tank Pressure Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming
    •  Evaporative Emission System Cleaning

Repair Verification

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 8 inches H2O.