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 Part 1:

Typical Enabling Conditions Part 2:

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 operating conditions. When the VSV for EVAP is used to purge the evaporative emissions from the fuel tank into the intake manifold, fumes are drawn from the fuel tank into the charcoal canister. The VSV for CCV has an additional function that relieves the pressure when the pressure inside the fuel tank has rapidly increased. Finally, the VSV for CCV is used in unison with the VSV for EVAP to create a vacuum inside the fuel tank and leak tests are performed using this vacuum.

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 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 the ambient temperature must be approximately between 50 to 95 °F.
b. The Intake Air Temp. (IAT) and the Engine Coolant Temp. (ECT) sensors indicate almost the same value.

c. Clear the DTCs.
- Disconnect the battery terminal or remove the EFI No. 1 and ETCS fuses for more than 60 sec.
- Readiness tests will show INCMPL (incomplete).

d. Drive the vehicle on a freeway. Write down the state of the Readiness Tests. They will change to COMPL as the EVAP 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 Test screen.

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

- To get there, go to Advanced OBD II, On-board Tests, Non-continuous Tests.
- If all of the tests in the time $02 category show "Pass", the EVAP 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 Test screen.

1. If all 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 DTC's are listed for the first trip.

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

Second Trip Procedure

e. The vehicle must be cold, and the ambient temperature must be approximately between 50 to 95 °F.
f. Go to Readiness Tests screen.
g. Drive the vehicle on a freeway. Write down the state of EVAP evaluation monitor. This procedure may take approximately 20 minutes or more.

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

h. If Readiness Tests changes to COMPL, the EVAP evaluation monitor has operated. Check for any stored DTCs.
- If a DTC has 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:
- If DTC P0441 (Purge Flow), P0446 (VSV for CCV), P0451, P0452 or P0453 (Evaporative Pressure Sensor) is output with DTC P0442 or P0456, first troubleshoot DTC P0441, P0446, P0451, P0452 or P0453. If no malfunction is detected, troubleshoot DTC P0442 or P0456 next.
- Ask the customer whether, after the MIL came on, the customer found the fuel tank cap loose and tightened it. Also ask the customer whether the fuel tank cap was loose when refuelling. If the fuel tank cap was loose, it was the cause of the DTC. If the fuel tank cap was not loose or if the customer was not sure if it was loose, troubleshoot according to the following procedure.
- 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, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
- If the ENGINE RUN TIME in the freeze frame data is less than 200 seconds, carefully check the vapor pressure sensor.

HINT: DTC output, malfunction indicates, and repair procedure.