Circuit Description
The DTC P0446 Evaporative Emissions (EVAP) Vent System Performance diagnostic monitors the performance of the EVAP system vent routine. Ignition voltage is supplied directly to the EVAP canister vent valve solenoid. The powertrain control module (PCM) closes the vent valve by grounding the solenoid control circuit using an internal solid state device called a driver. When the valve is closed, the FTP sensor will indicate a drop in pressure in the EVAP system during purge activity. If Fuel Tank Pressure (FTP) sensor values do not correspond with vent valve activity, a DTC P0446 will set.
Condition for Running the DTC
| • | Barometric pressure (BARO) is more than 75 kPa. |
| • | Engine coolant temperature (ECT) is between -8 and +110°C (18-230°F). |
| • | Intake air temperature (IAT) is more than -8°C (18°F) at engine start up. |
Conditions for Setting the DTC
The fuel tank pressure (FTP) sensor indicates a lower than expected pressure when EVAP vent valve is OFF.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with a active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL after 3 consecutive trips without a fault. |
| • | The PCM clears a history DTC after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
If a DTC P0446 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify if the fault is present. Refer to Inspection/Maintenance Evaporative Emission System Set .
Test the operation of the EVAP canister vent valve. Refer to Evaporative Emission Control System Diagnosis .
An intermittent malfunction may be caused by a fault in the electrical circuit of the EVAP canister vent valve . Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0446 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step checks the control circuit of the EVAP canister vent valve . The control of the EVAP canister vent valve is disabled by the PCM until there is no RPM indicated, and there are no DTCs set. The output controls can be found on the scan tool under Special Functions.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0446 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0446 appears in the Not Ran Since Code Cleared list, the DTC P0446 diagnostic has not yet run. When the DTC P0446 does not appear in the Not Ran Since Code Cleared list, the DTC P0446 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0446 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
2 |
Is the fuel tank pressure within the specified range with the fuel filler cap removed? | 0.0-0.9 mm Hg (0.0-0.5 in H2O) | Go to Step 3 | Go to DTC P0451 for FTP sensor diagnosis |
3 |
Is the resistance within the specified range? | 28 - 36 ohms at 20°C (68°F) | Go to Step 4 | Go to Step 11 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 |
Does the test lamp illuminate only when commanded ON with the scan tool? | -- | Go to Step 8 | Go to Step 6 | |
6 |
Was a repair necessary? | -- | Go to Step 13 | Go to Step 12 |
7 |
Is the action complete? | -- | Go to Step 13 | -- |
8 | Check the EVAP vent valve inlet air filter and line for blockage. Was a repair necessary? | -- | Go to Step 13 | Go to Step 9 |
9 | Check the EVAP canister for restrictions or blockages. Refer to Evaporative Emission Control System Diagnosis . Did the canister pass all tests? | -- | Go to Diagnostic Aids | Go to Step 10 |
10 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the action complete? | -- | Go to Step 13 | -- |
11 | Replace the EVAP canister vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Is the action complete? | -- | Go to Step 13 | -- |
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 13 | -- |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 | |
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
