GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Tahoe - 4WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0446

Description

A RESTRICTED or BLOCKED EVAP VENT PATH is detected by the powertrain control module (PCM) monitoring the fuel tank pressure (FTP) during normal operation. The PCM commands the evaporative emission (EVAP) vent valve OFF (open), and the EVAP canister purge valve ON (open). The fuel tank pressure should remain low as vacuum is drawn on the EVAP system. If the vent path is blocked or restricted, the vacuum level will increase and DTC P0446 will set.

Conditions for Running the DTC
    • DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0443, P0449, P0452, P0453, P1111, P1112, P1114, P1115, P1120, P1220, or P1221 are not set.
    • The system voltage is between 10-18 volts.
    • 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 fuel tank level is between 30-85 percent.
    • The barometric pressure (BARO) is more than 75 kPa.
    • The vehicle speed sensor (VSS) is less than 120.67 km/h (75 mph).

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

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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 vent valve inlet or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem. To repair a blockage in the EVAP system. Refer to Evaporative Emission System Cleaning .

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.

DTC P0446

Step

Action

Values

Yes

No

Schematic Reference: Emission Hose Routing Diagram and Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Did DTC P0443, P0449, P0452 or P0453 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Inspect the EVAP system for the following conditions:

    • A damaged EVAP vent valve
    • A pinched EVAP fresh air vent hose

Did you find and correct the condition?

--

Go to Step 12

Go to Step 4

4

  1. With a scan tool, review and record the Freeze Frame/Failure Records Data.
  2. With a scan tool, clear the DTC codes.
  3. Perform the Service Bay Test. Refer to Service Bay Test .

Does the scan tool indicate that the Service Bay Test has passed?

--

Go to Diagnostic Aids

Go to Step 5

5
  1. Disconnect the purge line from the EVAP purge valve.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the fuel tank pressure parameter.

Does the scan tool indicate fuel tank pressure near the specified value?

0 in. H2O

Go to Step 6

Go to Step 10

6
  1. Turn OFF the ignition.
  2. Reconnect all previously disconnected hardware.
  3. Install the J 41413 EVAP Pressure/Purge Diagnostic station and the J 41415 Fuel Tank Cap Adapter.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, seal the EVAP system.
  6. With the J 41413 , pressurize the EVAP system to the first specified value.
  7. Disconnect the EVAP vent hose from the EVAP vent valve.

Does the scan tool indicate fuel tank pressure near the second specified value?

5 in. H2O

0 in. H2O

Go to Step 8

Go to Step 7

7
  1. With the EVAP diagnostic station, maintain the first specified value.
  2. Disconnect the EVAP vapor pipe from the EVAP canister.

Does the scan tool indicate fuel tank pressure near the second specified value?

5 in. H2O

0 in. H2O

Go to Step 11

Go to Step 9

8

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

Did you complete the replacement?

--

Go to Step 12

--

9

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

Did you complete the replacement?

--

Go to Step 12

--

10

Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Repair the blockage in the EVAP vent hose.

Did you complete the repair?

--

Go to Step 12

--

12
  1. Reconnect all of the EVAP hardware that was previously disconnected.
  2. Perform the Service Bay Test. Refer to Service Bay Test .

Does the scan tool indicate that the Service Bay Test has passed?

--

Go to Step 13

Go to Step 3

13

With a scan tool, select the Review Info option

Does the scan tool indicate any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK