P0446

DTC P0446 Evaporative Emission Control System Vent Control Circuit

MONITOR DESCRIPTION

DTC Detection Condition:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result (Mode 06 Data):

The ECM tests the Evaporative Emissions (EVAP) system using the fuel tank pressure sensor, the Canister Close Valve (CCV), and the VSV for EVAP. The ECM closes the EVAP system and introduces a negative pressure (vacuum) into it. The ECM then monitors the internal pressure using the fuel tank pressure sensor (Refer to graphic).

P0446
The VSV for CCV is open under normal conditions. The VSV for EVAP is used to:
1. Purge the evaporative emissions from the fuel tank into the intake manifold before the VSV for CCV draws fumes from the fuel tank into the charcoal canister.
2. Relieve pressure inside the fuel tank when the pressure has suddenly risen.
3. Create a vacuum (negative pressure) inside the fuel tank and perform leak tests along with the VSV for EVAP.

The ECM checks for a VSV for CCV "stuck closed" malfunction by commanding both valves (VSV for EVAP and VSV for CCV) open at a time when the fuel tank is at atmospheric pressure. If the fuel tank develops a high negative pressure (vacuum), which remains in that state for more than 4 seconds, the ECM determines that the VSV for CCV (vent) is "stuck closed". The ECM will turn on the MIL and a DTC is set. This malfunction is detected regardless of the engine coolant temperature.

The ECM checks for a VSV for CCV "stuck open" malfunction by commanding both valves closed at a time when the fuel tank should have developed a high negative pressure (vacuum). If the fuel tank did not develop the proper high negative pressure (vacuum), the ECM concludes that the VSV for CCV must have been "stuck open". The ECM will turn on the MIL and a DTC is set.

Wiring Diagram:

CONFIRMATION READINESS TEST

First Trip Procedure
a. The vehicle must be cold, and ambient temperature is approximately between 10 °C (50 °F) and 35 °C (95 °F).
b. Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensors indicate almost the same value.

c. Clear DTCs.
- Disconnect the battery terminals or EFI fuse for more than 60 seconds.
- Readiness tests will show INCMPL (incomplete).
d. Drive the vehicle on a freeway. Write down the state of Readiness Tests. They will change to COMPL as the evaluation monitors operate and if the system passes. This procedure may take approximately 20 minutes or more.

NOTE: Do not shut off the engine - the results will be invalid.

Pass Condition - No Problem Found by the ECM
If the EVAP evaluation monitor shows COMPL, go to the Non-Continuous Tests screen.

NOTE: Do not shut off the engine - the results will be invalid.

- To enter the Non-continuous Tests, select Advanced OBD II / On-board Tests / Non-continuous Tests.
- If all of the tests in the time $02 category tests show "Pass", the evaluation monitor has operated and no problem was detected.

Fail Condition - Problem Detected by the ECM
If the EVAP evaluation monitor shows INCMPL, go to the Non-Continuous Tests screen.

1. If all of the tests show "Pass", the following may have occurred.
- The EVAP evaluation monitor did not operate.
- The EVAP evaluation monitor did not finish.
- The ECM withheld judgement.

2. If one or more of the tests in the time $02 category show "Fail", the EVAP evaluation monitor did operate and the ECM detected a problem.

3. Go to Continuous Tests screen. This is the only place which DTC's are listed for the first trip.

NOTE: The listed DTCs may not be valid. The second trip is needed to confirm the DTCs.

Second Trip Procedure

a. The vehicle must be cold, and the ambient temperature is approximately between 10 °C (SOT) and 35 °C (95 °F).
b. Go to Readiness Tests screen.
c. Drive the vehicle on a freeway. Write down the state of the EVAP evaluation monitor. This procedure may take approximately 20 minutes or more.

NOTE: Do not shut off the engine - the results will be invalid.

If Readiness Tests changes to COMPL, the EVAP evaluation monitor has operated. Check for any stored DTCs.
- If a DTC is stored, the problem has been detected and confirmed by the ECM.
- If no DTCs is found, the EVAP monitor operated but no problem was detected.

INSPECTION PROCEDURE

HINT:
- When using the hand-held tester, follow the procedures under the title "Hand-held tester".
- When using the OBD II scan tool, follow the procedures under the title "OBD II scan tool (excluding hand-held tester)" (See the procedures after the "Hand-held tester" procedures).
- Always troubleshoot DTCs P0441 (purge flow), P0446 (VSV for CCV), P0451, P0452 and P0453 (evaporative pressure sensor) before troubleshooting DTCs P0442 or P0456.
- As the customer the following questions:
1. Whether or not the fuel tank cap was loose and then tightened when the MIL came on.
2. Whether or not the fuel tank cap was loose when refueling. If the fuel tank cap was loose, it caused the DTC to be output. If the fuel tank cap was loose or the customer cannot remember, troubleshoot according to the procedures.

- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- If the ENGINE RUN TIME in freeze frame data is less than 200 seconds, carefully check the vapor pressure sensor.