P0446

DTC P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT

CIRCUIT DESCRIPTION

DTC Detection Condition:

The vapor pressure sensor and VSV for canister closed valve (CCV) are used to detect abnormalities in the evaporative emission control system.

The ECM decides whether there is an abnormality in the evaporative emission control system based on the vapor pressure sensor signal. DTCs P0441 and P0446 are recorded by the ECM when evaporative emissions leak from the components within the dotted line in figure 1, or when there is malfunction in either the EVAP VSV or the vapor pressure sensor itself.

HINT: Typical DTC output of each trouble part.

MONITOR DESCRIPTION

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 EVAP VSV. The ECM closes the EVAP system and introduces negative pressure (vacuum) into it. The ECM then monitors the internal pressure using the fuel tank pressure sensor.

P0446
If there is malfunction detected in the VSV for evaporative emission (EVAP), the canister closed valve (CCV) and the VSV for purge flow switching valve; the ECM will illuminate the MIL and set a DTC.
This portion of the EVAP diagnosis checks the following EVAP system functions:
a. CCV stuck closed.
The ECM checks for a CCV "stuck closed" malfunction by commanding the CCV to open after an EVAP leak test. If the fuel tank pressure does not rise (lose vacuum), the ECM determines that the CCV has stuck closed. The ECM will turn on the MIL and a DTC is set.
b. VSV for purge flow switching valve stuck closed.
The ECM checks for a VSV for purge flow switching valve "stuck closed" malfunction by commanding the VSV for purge flow switching valve to close after an EVAP leak test. If the fuel tank pressure does not change, the ECM determines that the VSV for purge flow switching valve is malfunctioning. The ECM will turn on the MIL and a DTC is set.
c. EVAP VSV (Purge line to intake manifold) stuck closed.
The ECM checks for a stuck closed malfunction in the EVAP VSV by commanding it to open with the CCV closed. If a high negative pressure does not develop in the fuel tank, the ECM determines that the EVAP VSV remains closed. The ECM turns 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 air temperature must be approximately 10 ° (50 °) to 35 °C (95 °F).
b. The Intake Air Temperature (IAT) and the Engine Coolant Temperature (ECT) sensors indicate almost the same value.

c. Clear the DTCs.
- 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 / ONBOARD 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 has 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 listed DTCs may be invalid. A second trip is needed to confirm listed DTCs.

Second Trip Procedure

e. The vehicle must be cold, and the ambient air temperature must be approximately 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 given in 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 (CCV), P0451, P0452 and P0453 (evaporative pressure sensor) before troubleshooting DTCs P0442 or P0456.
- Ask 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 why the DTC was stored.
If the fuel cap was not loose or if 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 condition when 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.