GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Tahoe - 2WD 🢒 DTC 🢒 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 Open and the EVAP canister vent solenoid 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 Closed and the EVAP canister vent solenoid 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 valves.

Control Module Command

EVAP Canister Purge Solenoid

EVAP Canister Vent Solenoid

ON

Open

Closed

OFF

Closed

Open

Conditions for Running the DTC
    • DTC P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0147, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0167, P0220, P0442, P0443, P0449, P0452, P0453, P0455, P0502, P0503, P1111, P1112, P1114, P1115, P1120 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 startup engine coolant temperature (ECT) is between 4-30°C (39-86°F).
    • The startup intake air temperature (IAT) is between 4-30°C (39-86°F).
    • The startup ECT and IAT are within 9°C (16°F) of each other.

Conditions for Setting the DTC
    • The fuel tank pressure sensor is less than -10 inches H2O.
    • The above condition is present for more than 30 seconds.

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
    • An intermittent condition could be caused by a damaged evaporative emission (EVAP) vent housing, a temporary blockage at the EVAP vent solenoid inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.
    • For intermittent conditions, refer to Intermittent Conditions

Test Description

The number below refers to the step number on the diagnostic table.

  1. This test determines if the failure is present or intermittent.

Step

Action

Values

Yes

No

Schematic Reference: Emission Hose Routing Diagram

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

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

    • A damaged EVAP vent solenoid--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 15

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the purge line from the EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .
  3. 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 4

Go to Step 9

4

Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  1. Turn OFF the ignition.
  2. Connect the EVAP purge pipe.
  3. Connect the J 41413-200 Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source.
  4. Install the J 41415-40 Fuel Tank Cap Adapter to the fuel fill pipe.
  5. Connect the fuel fill cap to the J 41415-40 .
  6. Connect the J 41413-200 nitrogen/smoke supply hose to the J 41415-40 .
  7. Turn ON the ignition, with the engine OFF
  8. Command the EVAP vent solenoid closed with a scan tool.
  9. Turn the nitrogen/smoke valve on theJ 41413-200 control panel to NITROGEN.
  10. Use the remote switch to pressurize the EVAP system to the first specified value.
  11. Observe the fuel tank pressure sensor in H2O with a scan tool.
  12. Command the EVAP vent solenoid open with a scan tool.

Is the fuel tank pressure sensor parameter less than the second specified value?

5 in H2O

1 in H2O

Go to Step 5

Go to Step 7

5
  1. Connect the nitrogen/smoke hose to the EVAP service port.
  2. Remove the J 41415-40 .
  3. Install the fuel fill cap to the fuel fill pipe.
  4. Start the engine.
  5. Allow the engine to idle.
  6. Use the purge/seal function to seal the system, with a scan tool.
  7. Command the EVAP canister purge solenoid valve to 30 percent.
  8. Observe the vacuum/pressure gage of the J 41413-200 until it reaches approximately 16 in H2O.
  9. Use the purge/seal function to seal the system, with a scan tool.

Is the FTP parameter on a scan tool within the specified value of the vacuum/pressure gage on the J 41413-200 , until the vacuum reached the abort limit on a scan tool?

1 in H2O

Go to Step 6

Go to Step 9

6

Did the FTP parameter on a scan tool display more than the specified value?

3.2 V

Go to Diagnostic Aids

Go to Step 9

7

Disconnect the EVAP vent hose from the EVAP vent solenoid.

Is the fuel tank pressure sensor parameter less than the specified value?

1 in H2O

Go to Step 13

Go to Step 8

8

Disconnect the EVAP vent hose from the EVAP canister.

Is the fuel tank pressure sensor parameter less than the specified value?

1 in H2O

Go to Step 11

Go to Step 14

9

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

Did you find and correct the condition?

--

Go to Step 15

Go to Step 10

10

Test for poor connections at the harness connector of the fuel tank pressure (FTP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

11

Repair the pinched or restricted EVAP vent hose.

Did you complete the repair?

--

Go to Step 15

--

12

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

Did you complete the replacement?

--

Go to Step 15

--

13

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

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15
  1. Turn OFF the ignition.
  2. Disconnect the purge line from the EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .
  3. 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 16

Go to Step 2

16

Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  1. Turn OFF the ignition.
  2. Reconnect all disconnected components.
  3. Connect the J 41413-200 to the fuel fill pipe.
  4. Turn ON the ignition, with the engine OFF
  5. Command the EVAP vent solenoid closed with a scan tool.
  6. Turn the nitrogen/smoke valve on theJ 41413-200 control panel to NITROGEN.
  7. Use the remote switch to pressurize the EVAP system to the first specified value.
  8. Observe the fuel tank pressure sensor in H2O with a scan tool.
  9. Command the EVAP vent solenoid open with a scan tool.

Is the fuel tank pressure sensor parameter less than the second specified value?

5 in H2O

1 in H2O

Go to Step 17

Go to Step 2

17

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK