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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Cobalt 🢒 Restraints 🢒 SIR 🢒 DTC P0446

System Description

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module 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 control module commands the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, this DTC sets.

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 solenoid valves.

Control Module Command

EVAP Canister Purge Solenoid

EVAP Canister Vent Solenoid

ON

Open

Closed

OFF

Closed

Open

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0446 Evaporative Emissions (EVAP) Vent System Performance

Conditions for Running the DTC
    • DTCs P0030, P0036, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0220, P0442, P0443, P0449, P0452, P0453, P0455, P0502, P0562, P0563, P0641, P0651, and P1133, P1134 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 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 8°C (14.4°F) of each other.
    • The vehicle speed sensor (VSS) is less than 137 km/h (85 mph).
    • The purge solenoid valve is enabled.
    • 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 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.
    • The fuel tank vacuum is greater than a calibrated amount for a calibrated period of time.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • The EVAP system tests run when the engine is first started and meets the Conditions for Running the DTC. An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP canister vent inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill condition.
    • 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 Filter Replacement and Evaporative Emission System Cleaning .
    • Disconnecting one component at a time while the EVAP system is under flow will help to pinpoint a restriction in the system.
    • Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
    • For intermittent conditions, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

Schematic Reference: Evaporative Emissions Hose Routing Diagram and Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Inspect the evaporative emission (EVAP) system for the following conditions:

    • A damaged EVAP vent solenoid valve--Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .
    • A pinched EVAP vent hose
    • A damaged EVAP canister--Refer to Evaporative Emission Canister Replacement .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 3

3
  1. Turn on the ignition
  2. Command the EVAP canister vent solenoid valve ON and OFF with a scan tool.

Do you hear or feel the EVAP canister vent solenoid valve click when commanded ON and OFF?

--

Go to Step 5

Go to Step 4

4
  1. Remove the EVAP canister vent solenoid valve from the EVAP canister. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .
  2. Connect the EVAP canister vent solenoid valve electrical connector.
  3. Command the EVAP vent solenoid valve ON and OFF with the scan tool.

Does the EVAP canister vent solenoid valve operate when it is commanded ON and OFF?

 

Go to Step 5

Go to Step 12

5
  1. Turn OFF the ignition.
  2. Install the EVAP canister vent solenoid valve if removed in previous step.
  3. Disconnect the EVAP purge pipe from the EVAP purge solenoid valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .
  4. Turn ON the ignition, with the engine OFF.

Is the Fuel Tank Pressure Sensor parameter within the specified range?

-1 to +1 in H2O

Go to Step 6

Go to Step 14

6

Important: 

   • DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
   • Refer to the J 41413-200 Evaporative Emissions System Tester (EEST) operation manual for detailed instructions.

  1. Turn OFF the ignition.
  2. Connect the EVAP purge pipe.
  3. Using the GE-41415-50 Fuel Tank Cap Adapter, connect the J 41413-200 to the vehicle's fuel filler neck.
  4. Turn ON the ignition, with the engine OFF.
  5. Command the EVAP canister vent solenoid valve closed with a scan tool.
  6. Use the J 41413-200 to pressurize the EVAP system with NITROGEN to the first specified value.
  7. Observe the Fuel Tank Pressure Sensor parameter with a scan tool.

Is the Fuel Tank Pressure Sensor parameter more than the second specified value?

10 in H2O

5 in H2O

Go to Step 7

Go to Step 13

7
  1. Start the engine with the J 41413-200 still connected to the fuel filler neck.
  2. Allow the engine to idle.
  3. Use the Purge/Seal function to seal the system with a scan tool.
  4. Command the EVAP canister purge solenoid valve to 30 percent.
  5. Observe the vacuum/pressure gage on the J 41413-200 and the FTP parameter on the scan tool.
  6. Allow the vacuum to increase on the gage of the J 41413-200 until it reaches approximately 16 inches H2O or until the vacuum reached the abort limit on the scan tool.
  7. Use the Purge/Seal function to seal the system with a scan tool.

Was the difference between the FTP parameter on a scan tool and the vacuum/pressure gage on the J 41413-200 less than the specified value?

1 in H2O

Go to Step 8

Go to Step 14

8

Did the Fuel Tank Pressure Sensor parameter on a scan tool display more than the specified value?

3.2 V

Go to Step 9

Go to Step 14

9

Important: 

   • DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
   • Refer to the J 41413-200 operation manual for detailed instructions.

  1. Turn ON the ignition with the engine OFF
  2. Use the J 41413-200 to pressurize the EVAP system with NITROGEN to the first specified value.
  3. Command the EVAP canister vent solenoid valve open.

Does the Fuel Tank Pressure sensor parameter return to the second specified value?

5 in H2O

-1 to +1 in H2O

Go to Step 10

Go to Step 17

10
  1. Turn ON the ignition with the engine OFF
  2. Use the J 41413-200 to pressurize the EVAP system with NITROGEN.

With NITROGEN flowing and the EVAP canister vent solenoid valve OPEN, does the Fuel Tank Pressure Sensor parameter remain below the specified value?

3 in H2O

Go to Step 11

Go to Step 17

11
  1. Start the engine.
  2. Allow the engine to idle.
  3. With the EVAP canister vent solenoid valve OPEN, command the EVAP canister purge solenoid valve to 100 percent with a scan tool.

Does the Fuel Tank Pressure sensor parameter display more vacuum than the specified value?

-5 in H2O

Go to Step 17

Go to Diagnostic Aids

12
  1. Disconnect the EVAP canister vent solenoid valve.
  2. Command the EVAP canister vent solenoid valve OFF.
  3. Probe the control circuit of the EVAP canister vent solenoid with a test lamp that is connected to battery positive.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 18

13

Test the EVAP canister vent solenoid control circuit for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

14

Test for an intermittent and for a poor connection at the fuel tank pressure (FTP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 15

15

Test the low reference circuit of the FTP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

16

Test for an intermittent and for a poor connection at the control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

17

Inspect the EVAP vent system for a restriction.

Did you find and correct the condition?

--

Go to Step 21

Go to Diagnostic Aids

18

Replace the EVAP canister vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .

Did you complete the replacement?

--

Go to Step 21

--

19

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the engine control module (ECM). Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 21

--

21
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 60 seconds.
  3. Start the engine.
  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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 22

22

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK