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P0446




DTC P0446

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P0446
- Evaporative Emissions (EVAP) Vent System Performance

Circuit/System Description

The control module tests the evaporative emission (EVAP) system for a restricted or blocked vent path. The ECM detects a blockage or restriction by commanding the purge valve ON (open) and the vent valve ON (closed) allowing a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the purge valve OFF (closed) and the vent valve OFF (open) while monitoring the fuel tank pressure (FTP) sensor for a decrease in vacuum.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves.





Conditions for Running the DTC

* Before the ECM can report DTC P0446 failed, DTCs P0450, P0451, P0452, and P0453 must run and pass.
* DTC P0100, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0221, P0222, P0223, P0443, P0449, P0451, P0452, P0453, P0458, P0459, P0496, P0497, P0498, P0499, P0560, P0562, P0563, P0700, P2122, P2123, P2127, P2128 or P2138 is not set.
* The ignition voltage is 10-18 V.
* The Closed Loop fuel control is enabled.
* The engine run time is greater than 10 min or the fuel trim is stable.
* The engine is idling.
* The FTP is between -18.7 and +9.8 mm Hg (-10.0 and +5.2 in. H2O).
* The ambient air temperature (AAT) is between 2-32°C (35-90°F).
* The ECT and the IAT are within 10°C (18°F) of each other at engine start-up.
* The barometric pressure (BARO) is greater than 68 kPa.
* The long term fuel trim remains steady, less than 3 % change in 200 ms over a period of 8 s.
* The fuel level is between 11-88 %.
* The vehicle speed sensor (VSS) is less than 3 km/h (2 mph).
* The above conditions exist for greater than 5 s.
* DTC P0446 will attempt to run up to 10 times or until the test completes successfully once per ignition cycle.

Conditions for Setting the DTC

* The FTP is less than -7.5 mm Hg (-4.0 in. H2O).
* The condition is exists for greater than 4 s or a cumulative of 30 s.

Action Taken When the DTC Sets

DTC P0446 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0446 is a Type B DTC.

Diagnostic Aids

An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet or a pinched vent hose. A blockage in the vent system may also cause a poor fuel fill problem.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Evaporative Emission Control System Description (Evaporative Emission Control System Description)
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON and fuel cap removed, verify that the Fuel Tank Pressure Sensor parameter is between 1.3-1.7 volts.

• If not within the specified range, go to the fuel tank pressure sensor section in Circuit/System Testing.

2. Install the fuel cap.
3. With the engine running, the EVAP canister vent solenoid valve open, use a scan tool to command the EVAP canister purge solenoid valve to 100 percent. The fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).

• If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.

4. Using the scan tool, decrease the canister purge duty cycle from 100 percent to 0 percent. The vacuum should decrease to near zero.

• If the fuel tank vacuum does not return to zero or appears to decrease too slowly go to the restriction section in Circuit/System Testing.

5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Note: Perform the Circuit/System Verification before proceeding with the Circuit/System Testing.

Restriction
1. With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).

• If the fuel tank vacuum is greater than the specified value, isolate the restriction by disconnecting one component at a time while the EVAP canister purge solenoid valve is commanded to 100 percent and the vent valve is open.

2. Using the scan tool, decrease the canister purge duty cycle from 100 percent to 0 percent. The vacuum should decrease to near zero.

• If the fuel tank vacuum does not return to zero, or appears to decrease too slowly, inspect the components in the EVAP vent system for a restriction.

Fuel Tank Pressure Sensor
1. Ignition OFF, disconnect the harness connector at the fuel tank pressure sensor.
2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the fuel tank pressure sensor.

Repair Instructions

Evaporative Emission Canister Vent Solenoid Valve Replacement (Service and Repair)

Repair Verification

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

With the engine running, the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).

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