GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Savana 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0446

Description

A restricted or blocked evaporative emission (EVAP) vent path is detected by the powertrain control module (PCM) monitoring the fuel tank pressure during normal operation. The PCM commands the EVAP vent valve OFF, or open, and the EVAP canister purge valve ON, or 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
    • DTC P0107. P0108, P0110, P0112, P0113, P0115, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0442, P0443, P0449, P0452, P0453, P1106. P1107, P1111, P1112, P1114, P1115, P1121, and P1122 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 75 mph.

Conditions for Setting the DTC
    • The fuel tank pressure (FTP) 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, by a temporary blockage at the EVAP vent valve inlet, or by a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem. In order 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.

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

Did DTCs P0443, P0449, P0452, or P0453 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.
  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 FTP parameter.

Does the scan tool indicate FTP 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 Adaptor.
  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 FTP near the second specified value?

5 in H2O

0 in H2O

Go to Step 8

Go to Step 7

7
  1. With the J 41413 , maintain the first specified value.
  2. Disconnect the EVAP vapor pipe from the EVAP canister.

Does the scan tool indicate FTP 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 FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Repair for a 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

Use a scan tool in order to observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK