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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

Object Number: 383813 Size: MF
Engine Controls Component Views
Cell 20: Evaporative Emissions Vent Valve Solenoid
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM monitors the performance of the EVAP system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this DTC if the vacuum decay rate exceeds a predetermined amount of time.

Conditions for Running the DTC

    •  DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0420, P0430, P0500, P0502, P0503, P0562, P0563, P1120, P1220, P1221, and HO2S DTCs are not set.
    • The ignition voltage is between 10 and 18 volts.
    • The barometric pressure is more than 75 kPa.
    • The fuel level is between 15% and 85% of full capacity.
    • The engine coolant temperature is between 4°C (39°F) and 30°C (86°F).
    • The intake air temperature is between 4°C (39°F) and 30°C (86°F).
    • The start up engine coolant temperature and the intake air temperature are within 9°C (16°F) of each other.

Conditions for Setting the DTC

    • The EVAP vacuum decay rate is greater than a predetermined value when the PCM commands the vent solenoid open.
    • The conditions are present for greater than 2.0 seconds.

OR

    • The vacuum present in the EVAP system is greater than a predetermined value when the vent solenoid is command open during normal purge.
    • The conditions are present for greater than 4.0 seconds.

Important: This DTC does not report a first failed test. A first fail of this DTC will have a scan tool status as Not Run. Use the scan tool data display parameter of EVAP Test Result to determine if this DTC has failed or passed for this ignition cycle.

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

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids

Important: 

   • Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
   • For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

    • An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTC's before performing this diagnostic table. Always monitor for fuel level sensor DTCs stored as History.
    • The Service Bay Test may have to be performed in cold ambient air temperatures when the vehicle is running a winter grade fuel. The scan tool displays a message when the service bay test does not run.
    • Perform a physical inspection of the EVAP system. Inspect for the following conditions:
       - A loose, missing, defective, or incorrect fuel tank cap
       - Incorrectly routed or defective EVAP system vacuum and vapor lines
       - A malfunctioning or damaged vapor canister
    • Inspect for charcoal release from the vapor canister. Refer to the Evaporative Emission System Cleaning procedure.
    • The vacuum and pressure in the EVAP system is measured in inches of H2O (water). Most gauges measure vacuum in inches of Hg (mercury) and pressure in psi (pounds per square inch). The following table illustrates how the values compare:

in. H2O

in. Hg.

psi

1 in. H2O

0.07 in. Hg

0.0361 psi.

5 in. H2O

0.36 in. Hg

0.180 psi.

10 in. H2O

0.73 in. Hg

0.361 psi.

15 in. H2O

1.10 in. Hg

0.541 psi.

Conditions for Running the Service Bay Test

    • The battery voltage is between 10.5 and 18.0 volts.
    • The fuel level is between 15% and 85% of the full capacity.
    • The engine temperature is between 3.5°C (38°F) and 35°C (95°F).
    • Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.
    • For an intermittent, refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

  1. An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test. If the Service Bay Test can not be run, you must allow the vehicle to set until the conditions are met.

    2.

  2. An open in the Fuel Tank Pressure sensor ground circuit causes a high Fuel Tank Pressure sensor voltage. An open ground circuit may cause DTC P0446 to set. Refer to DTC P0453 for further diagnosis.

    3.

  3. This step verifies that the Fuel Tank Pressure sensor responds to a change in vacuum.

    4.

  4. This step isolates the EVAP system from the Fuel Tank Pressure sensor. A Fuel Tank Pressure sensor that does not correctly respond to pressure (or vacuum) causes this DTC to set.

    The Fuel Tank Pressure sensor range is from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).

    5.

  5. This step is testing the vapor canister and the EVAP Vent Valve for a restriction.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: Ensure that The Conditions for Running the Service Bay test are met before proceeding with this diagnostic. Refer to Diagnostic Aids.

Perform the EVAP system Service Bay Test.

Does the vehicle pass the Service Bay Test?

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Remove the fuel tank cap.
  3. Turn ON the ignition leaving the engine OFF.
  4. Monitor the Fuel Tank Pressure sensor voltage using a scan tool.

Is the Fuel Tank Pressure sensor voltage less than the specified value?

4V

Go to Step 4

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

4

Important: The DTCs must be cleared from the PCM in order to use the output control function on the scan tool.

  1. Clear the DTCs using a scan tool.
  2. Install the fuel tank cap.
  3. Start and idle the engine.
  4. Command the EVAP Purge solenoid to 50% using a scan tool.
  5. Monitor the fuel tank pressure using a scan tool.

Does the Fuel Tank Pressure change when the EVAP Canister Purge Solenoid is enabled?

--

Go to Step 6

Go to Step 5

5
  1. Turn OFF the engine leaving the ignition ON.
  2. Remove the left side wheel house panel. Refer to Wheelhouse Panel Replacement in Body Rear End.
  3. Disconnect the vacuum line from the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .
  4. Connect the hand held vacuum pump J 23738-A to the vacuum port of the Fuel Tank Pressure sensor.
  5. Attempt to apply a vacuum up to the specified value using the hand vacuum pump J 23738-A .
  6. Monitor the Fuel Tank Pressure using a scan tool.

Does the Fuel Tank Pressure change as vacuum is applied?

10 in Hg

Go to Step 6

Go to Step 13

6

Important: Do not overlook any items which could cause a DTC to set. Thoroughly inspect accessible components/pipes.

  1. Remove the left side wheel house panel. Refer to Wheelhouse Panel Replacement in Body Rear End. Removing the wheel house panel allows access the Fuel Tank Pressure sensor/pipes.
  2. Inspect the EVAP system for the following conditions:
    3. • Improperly routed, kinked or damaged EVAP purge and tank vent lines.
    • A damaged EVAP system component.
  3. Repair the EVAP system as necessary if you find a condition.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 7

7

Important: 

   • Do not overlook any items which could cause a DTC to set. Inspect for the following conditions while removing the right side fuel tank:
      - Kinked or pinched lines/pipes
      - Damaged hoses\pipes\components
      - Damaged O ring seals
   • The DTCs must be cleared from the PCM in order to use the output control function on the scan tool.

  1. Clear the DTCs using a scan tool.
  2. Turn OFF the ignition.
  3. Disconnect the electrical harness from the left side fuel tank sending unit.
  4. Remove the right side fuel tank. Refer to Fuel Tank Replacement .
  5. Disconnect the fuel tank vapor and the EVAP purge line from the EVAP canister.
  6. Plug the Canister port for the fuel tank vapor line using an appropriate plug.
  7. Connect the hand held vacuum pump J 23738-A to the EVAP purge line canister fitting.
  8. Turn ON the ignition leaving the engine OFF.
  9. Command the EVAP Vent Valve ON (closed) using the scan tool.
  10. Attempt to apply and hold the specified amount of vacuum using the hand held vacuum pump.
  11. Command the EVAP Vent Valve OFF (open) while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the EVAP Vent Valve is opened?

5 in. Hg.

Go to Step 10

Go to Step 8

8
  1. Leave the system as connected in Step 7.
  2. Disconnect the vent line at the EVAP Vent Valve.
  3. Plug the vent line using an appropriate plug.
  4. Attempt to apply and hold the specified amount of vacuum using the hand held vacuum pump J 23738-A .
  5. Remove the plug from the vent line while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the vent line is unplugged?

5 in. Hg.

Go to Step 12

Go to Step 9

9
  1. Inspect the EVAP Vent line from the canister to the EVAP Vent Valve for restrictions.
  2. If you find a condition repair as necessary.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

10

Repair the restriction between the Fuel Tank Pressure sensor and the EVAP canister.

Is the action complete?

--

Go to Step 14

--

11

Replace the EVAP Vent Valve. Refer to Evaporative Emission Vent Valve Replacement .

Is the action complete?

--

Go to Step 14

--

12

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

Is the action complete?

--

Go to Step 14

--

13

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

Is the action complete?

--

Go to Step 14

--

14

Important: Ensure that The Conditions for Running the Service Bay test are met before proceeding with this diagnostic. Refer to Diagnostic Aids.

Perform the EVAP system Service Bay Test using a scan tool.

Does the EVAP diagnostic pass the Service Bay Test?

--

Go to Step 15

Go to Step 3

15

Select the Capture Info option and the Review Info option using the scan tool.

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

--

Go to the applicable DTC

System OK