GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2007 🢒 SKY 🢒 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 Emission (EVAP) Vent System Performance

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.

FTP Sensor Signal Voltage

Fuel Tank Pressure

Low, Approximately 1.5 V or less

Positive Pressure

High, Approximately 1.5 V or more

Negative Pressure/Vacuum

Conditions for Running the DTC
    • DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0128, P0222, P0223, P0443, P0449, P0452, P0453, P0455, P0496, P0502, P0560, P0562, P0563 are not set.
    • The ignition voltage is between 11-18 volts.
    • The barometric pressure (BARO) is more than 68 kPa.
    • The fuel level is between 15-85 percent.
    • The estimated ambient air temperature is between 2-32°C (35.6-90°F).
    • The start-up ECT and estimated ambient air temperature are within 9°C (16.2°F) of each other.
    • The vehicle speed sensor (VSS) is less than 1.7 km/h (2 mph).
    • The purge solenoid valve is enabled.
    • DTC P0446 will attempt to run up to 10 times until it successfully completes.
    • DTC P0446 completes one test per trip when the above conditions have been met.

Conditions for Setting the DTC

The fuel tank pressure (FTP) sensor is more than 3 inches H2O vacuum for 4 seconds during the 10 minute test.

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 filter that is restricted can cause this DTC to set. Refer to Evaporative Emission System Cleaning .

Reference Information

Schematic Reference

    •  Evaporative Emissions Hose Routing Diagram
    •  Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls 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

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

Special Tools Required

    • GE-41415-50 Interrupted Thread Fuel Tank Cap Adapter
    • J 41413-200 Evaporative Emissions System Tester (EEST)

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 8 inches H2O.
    4. ⇒If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.

Circuit/System Testing

Important: Refer to the J 41413-200 operation manual for detailed instructions.

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 ON and fuel cap removed, verify that the FTP sensor parameter is between 1.3-1.7 volts.
    2. ⇒If the FTP sensor parameter is not within the specified range, test the FTP low reference circuit for an open or high resistance. If the circuit tests normal, replace the FTP sensor.
  2. With the GE-41415-50 , connect the J 41413-200 to the fuel filler neck.
  3. Start the engine.
  4. Allow the engine to idle.
  5. Use the Purge/Seal function to seal the system with a scan tool.
  6. Command the EVAP canister purge solenoid valve to 20 percent.
  7. Observe the vacuum/pressure gage on the J 41413-200 and the FTP parameter on the scan tool.
  8. Verify that the vacuum increases to the abort limit on the scan tool or more than 3.2 volts, and the value is closely similar between the scan tool and the vacuum/pressure gage on the J 41413-200 .
    9. ⇒If the values are not similar or the voltage is not within the specified range, replace the FTP sensor.

Repair Instructions
    •  Fuel Tank Pressure Sensor Replacement
    •  Control Module References for engine control module (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.