GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0446

Circuit Description

A restricted or blocked evaporative emission (EVAP) vent path is detected by the control module commanding the purge valve ON (open) and the vent valve ON (closed) allowing a vacuum to be applied to the EVAP system> Once a calibrated vacuum level has been reached, the control module commands the purge valve OFF (closed) and the vent valve OFF (open) while monitoring 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, DTC P0446 will set.

Conditions for Running the DTC
    • DTC P0107. P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0442, P0443, P0449, P0452, P0453, P1111, P1112, P1114, P1115, P1121, and P1122 not active.
    • 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 start up ECT and IAT are within 9°C (16°F) of each other.
    • 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 121 km/h (75 mph).

Conditions for Setting the DTC
    •  Fuel tank pressure is less than -10 in. 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

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.

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 DTC 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:

    • Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
    • A damaged EVAP vent valve.
    • A pinched EVAP vent hose.

Did you find and correct the condition?

--

Go to Step 14

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 8

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 41415-40 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 EVAP Diagnostic station, 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 10

Go to Step 7

7

Disconnect the EVAP vent hose from the EVAP canister.

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

0 in H2O

Go to Step 13

Go to Step 11

8

With a scan tool, observe the fuel tank pressure sensor voltage.

Is the FTP sensor voltage more than the specified value?

4.3 V

Go to DTC P0453

Go to Step 9

9

Test for poor connections at the harness of the fuel tank pressure 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 14

Go to Step 12

10

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

Did you complete the replacement?

--

Go to Step 14

--

11

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

Did you complete the replacement?

--

Go to Step 14

--

12

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

Did you complete the replacement?

--

Go to Step 14

--

13

Repair for a blockage in the EVAP vent hose.

Did you complete the repair?

--

Go to Step 14

--

14
  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 15

Go to Step 3

15

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