P0446

DTC P0446 Evaporative Emission Control System Vent Control Circuit

DESCRIPTION

DTC Detection Condition:

When predetermined conditions (closed loop, etc.) are met, the EVAP VSV is opened and stored fuel vapor in the canister is purged to the intake manifold. The ECM changes duty-cycle to the EVAP VSV to control purge flow volume. Purge flow volume is determined by the intake manifold pressure. Atmospheric pressure is allowed into the canister through the vent valve (CCV) to ensure that purge flow is maintained when negative pressure (vacuum) is applied to the canister. This EVAP system contains the given components.

MONITOR DESCRIPTION

Monitor Strategy (Part 1):

Monitor Strategy (Part 2):

Typical Enabling Conditions:

Typical Malfunction Thresholds:

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

The CCV is open under normal conditions. The CCV has the following features:
1. Draws fumes from the fuel tank into the charcoal canister after the EVAP VSV purges the EVAP from the fuel tank into the intake manifold,.
2. Relieves pressure inside the fuel tank when the pressure has suddenly risen.
3. Works with the EVAP VSV to create negative pressure (vacuum) inside the fuel tank and performs leak tests.

The ECM checks if the CCV is "stuck closed". The ECM commands the CCV to open while the EVAP VSV is open. If high negative pressure (vacuum) develops in the fuel tank and stays for more than 4 seconds, the ECM determines that the CCV remains closed despite the open command. The ECM will turn on the MIL and set a DTC. The engine coolant temperature is not related to the output of this DTC.

The ECM also has a method for checking if the CCV is "stuck open". The ECM commands the CCV to close while the EVAP VSV is open. If a sufficient amount of negative pressure does not develop in the fuel tank, the ECM determines that the CCV remains open despite the close command. The ECM will turn on the MIL and set a DTC.

MONITOR RESULT

Refer to "CHECKING MONITOR STATUS" for detailed information. Mode 6 Data

The test value and test limit information are described as shown in the given table. Check the monitor result and test values after performing the monitor drive pattern.

Part 1:

Part 2:

- TID (Test Identification Data) is assigned to each emissions-related component.
- TLT (Test Limit Type):
If TLT is 0, the component is malfunctioning when the test value is higher than the test limit.
If TLT is 1, the component is malfunctioning when the test value is lower than the test limit.
- CID (Component Identification Data) is assigned to each test value.
- Unit Conversion is used to calculate the test value indicated on generic OBD II scan tools.