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 Emission (EVAP) Vent System Performance
Typical Scan Tool Data
Circuit/System Description
This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path that would cause excess amounts of vacuum to be developed in the EVAP system. With the purge valve open and the canister vent valve open, if EVAP system vacuum goes above a calibrated threshold, the test will fail.
Conditions for Running the DTC
* DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0220, P0222, P0223, P0443, P0449, P0452, P0453, P0502, P0503 are not set.
* The ignition voltage is between 11-18 volts.
* The barometric pressure (BARO) is more than 74 kPa.
* The fuel level is between 15-85 percent.
* The start-up engine coolant temperature (ECT) is less than 35°C (95°F).
* The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
* The start-up ECT and IAT are within 8°C (14.4°F) of each other.
* The purge solenoid valve is enabled.
* DTC P0446 runs once per trip when the above conditions have been met.
Conditions for Setting the DTC
* The FTP sensor is more than 12 inches H2O vacuum for 5 seconds.
OR
* The FTP is less than -2.5 inches H2O or more than +5 inches H2O 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 EVAP vent housing, a temporary blockage at the EVAP canister vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.
* An EVAP canister that is restricted can cause this DTC to set.
Reference Information
Schematic Reference
* Evaporative Emissions Hose Routing Diagram ([1][2]Diagrams)
* Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Evaporative Emission Control System Description (Evaporative Emission Control System Description)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Programming and Relearning (Programming and Relearning) for scan tool information
Special Tools
* GE-41415-50 Interrupted Thread Fuel Tank Cap Adapter
* J 41413-200 Evaporative Emissions System Tester (EEST)
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
* Fuel Tank Pressure Sensor Replacement (Service and Repair)
* Programming and Relearning (Programming and Relearning) for engine control module (ECM) replacement, setup, and programming
Repair Verification
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).