P0446
DTC P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUITCIRCUIT 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 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 these components:
MONITOR DESCRIPTION
DTC Detection Condition:
Monitor Strategy:
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 (refer to the graphic on page 05-195).
P0446 (FOR SYSTEM DIAGRAM AND DTC DETECTION TIMING CHART, REFER TO DTC P0441)
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 dose 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.
MONITOR RESULT
Refer to CHECKING MONITOR STATUS for detailed information.
The test value and test limit information are described as shown in the table. Check the monitor result and test values after performing the monitor drive pattern.
- 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.
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Step 4 (Contd.):
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Step 9:
Step 9 (Contd.):
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Step 12:
Step 13:
Step 14 - 15:
Step 16 - 17:
Step 17 (Contd.) - 20:
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Step 24 - 25:
Step 25 (Contd.) - 27:
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Step 31 - 32:
Step 33:
Step 34 - 35:
Step 36 - 37:
Step 38 - 39:
Step 40:
INSPECTION PROCEDURE
HINT: Read freeze frame data. Freeze frame data records 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.