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DTC P0446

DTC P0446

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptor

DTC P0446

Evaporative Emissions Vent System Performance

Typical Scan Tool Data

Fuel Tank Pressure Sensor Signal Voltage Fuel Tank Pressure
1.5 V Atmospheric Pressure/BARO
Less than 1.5 V Positive Pressure
More than 1.5 V Negative Pressure/Vacuum


Circuit/System Description

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked evaporative emission vent path that would cause excess amounts of vacuum to be developed in the evaporative emission system. With the purge valve open and the canister vent valve open, if the evaporative emission system vacuum goes above a calibrated threshold, the test will fail.

Conditions for Running the DTC


• DTCs P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0442, P0443, P0449, P0451, P0452, P0453, P0454, P0464, P0496, P0608, P0609, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138 are not set.

• The ignition voltage is between 11-18 V.

• The barometric pressure (BARO) is more than 74 kPa.

• The fuel level is between 15-85 percent.

• The engine coolant temperature (ECT) is less than 35°C (95°F).

• The intake air temperature (IAT) is between 4-30°C (39-86°F).

• DTC P0446 runs once per cold start when the above conditions are met.


Conditions for Setting the DTC


• The fuel tank vacuum is greater than 12 inches H2O vacuum for 5 seconds.

OR

• The fuel tank pressure is less than -2.5 inches H2O or more than +5 inches for 60 seconds after a cold start.


Action Taken When the DTC Sets

DTC P0446 is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P0446 is a Type B DTC.

Diagnostic Aids


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

• An evaporative emission canister filter that is restricted can cause this DTC to set.


Reference Information

Schematic Reference

Engine Controls Schematics (3.0L (LF1)) Engine Controls Schematics (2.8L (LAU))

Connector End View Reference

Component Connector End Views

Description and Operation

Evaporative Emission Control System Description

Electrical Information Reference


• Circuit Testing

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References 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.

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

3. Install the fuel cap.

4. 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).

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

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

7. 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.

8. 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).

2. 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.

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

4. 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.

3. 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 (NT7, NU5)

• Evaporative Emission Canister Replacement (NT7, NU5)

• Fuel Tank Pressure Sensor Replacement

• Control Module References


Repair Verification

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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