DTC P0446 Evaporative Emission Control System Vent Control Circuit

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 diagram Leak Check).

P0446

The VSV for CCV open under normal conditions. The VSV for CCV is used to:
1. After the VSV for EVAP purges the evaporative emissions from the fuel tank into the intake manifold, the VSV for CCV draws fumes from the fuel tank into the charcoal canister.
2. Discharge pressure inside the fuel tank when the pressure has suddenly risen.
3. Along with the VSV for EVAP, it creates a vacuum (negative pressure) inside the fuel tank and performs leak tests.

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) and it 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 the VSV for EVAP open with the VSV for CCV closed 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 the ambient temperature must be approximately between 50 to 95 °F.
b. The Intake Air Temperature (IAT) and the Engine Coolant Temperature (ECT) sensors indicate almost the same value.

c. Clear the DTCs.
- Disconnect the battery terminal or remove the EFI and ETCS fuses for more than 60 seconds.
- READINESS TESTS will show INCMPL (incomplete).

d. Drive the vehicle on a freeway. Write down the initial status of the READINESS TESTS. As each Readiness Test passes EVAP evaluation monitors, its status will change to COMPL (complete). 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.
- Enter the following menus: ADVANCED OBD II / ON-BOARD TESTS / NON-CONTINUOUS.

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

If all of the tests in the "Time $02" category show "Pass", the EVAP evaluation monitor detected no problem.

Fail Condition - Problem Detected by the ECM

If the EVAP evaluation monitor shows COMPL, go to the NON-CONTINUOUS TESTS screen.

1. If all tests show "Pass", one of the following may have occurred:
- The EVAP evaluation monitor did not operate.
- The EVAP evaluation monitor did not finish its tests.
- The ECM has 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 the CONTINUOUS TESTS screen. This is the only place DTCs are listed for the first trip.

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

Second Trip Procedure

e. The vehicle must be cold, and the ambient temperature must be approximately between 50 to 95 °F.

f. Go to the READINESS TESTS screen.

g. Drive the vehicle on a freeway. Write down the initial status of the READINESS TESTS. This procedure may take approximately 20 minutes or more.

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

h. If the READINESS TESTS change to COMPL, the EVAP evaluation monitor has operated. Check for any stored DTCs.
- If a DTC was stored, the problem has been detected and confirmed by the ECM.
- If no DTC was 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. When the MIL came on, if the fuel tank cap was loose and if it was then tightened.
2. When refueling, if the fuel tank cap was loose.

If the fuel tank cap was loose, that is the why the DTC was stored.
If the fuel cap was not loose or if the customer cannot remember, troubleshoot according to the procedures on the following.

- 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 the freeze frame data is less than 200 seconds, carefully check the vapor pressure sensor.

HINT: Use the chart above to check the malfunction for each DTC output. Then perform the necessary repairs listed under trouble chart.