DTC P0446 Evaporative Emission Control System Vent Control Circuit

DTC P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT

CIRCUIT DESCRIPTION










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 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 components as shown.

Contents:

Related DTCs Of EVAP:

Step 1:

Step 2 - 4:

INSPECTION PROCEDURE

MONITOR DESCRIPTION

DTC Detection Condition:

DTC Detection Condition:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result (Mode 06):

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.

P0446
The CCV is open under normal conditions. The CCV has the following features:
1. After the EVAP VSV purges the EVAP from the fuel tank into the intake manifold, the CCV draws fumes from the fuel tank into the charcoal canister.
2. Relieves pressure inside the fuel tank when the pressure has suddenly risen.
3. Along with the EVAP VSV, creates 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 would then turn on the MIL and output 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 would then turn on the MIL and output a DTC.