Diagnostic Instructions
DTC Descriptor
DTC P0446: Evaporative Emissions (EVAP) Vent System Performance
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 the EVAP system
vacuum goes above a calibrated threshold, the test will fail.
FTP 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
|
Conditions for Running the DTC
• | DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0125, P0128, P0443, P0449, P0451, P0453, P0454, P1106, P1107, P1111, P1112, P1114, P1115, P1125, P1516, P2101, P2108, P2119, P2120, P2125, P2138 are not set. |
• | The ignition voltage is between 10-18 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 30°C (86°F). |
• | The start-up intake air temperature (IAT) is less than 30°C (86°F). |
• | The start-up ECT and IAT are within 9°C (16°F) of each other. |
• | DTC P0446 runs once per trip when the above conditions have been met. |
Conditions for Setting the DTC
• | The fuel tank pressure (FTP) sensor is more than 8 inches H2O vacuum for 2 seconds during the 13 minute test. |
| The FTP is less than -2.5 inches H2O or more than +5 inches H2O for 3 seconds after a cold start ignition ON. |
• | The fuel tank vacuum is greater than a calibrated amount for a calibrated period of time. |
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, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using a purge solenoid command with a scan tool will allow vacuum to be applied to the system instead of pressure. 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 8 inches H2O. |
• | Disconnecting one component at a time while the EVAP system is under flow will help to pinpoint a restriction in the system. |
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON and fuel cap removed, verify that the FTP Sensor parameter is between 1.3-1.7 volts.
⇒ | If not within the specified range, go to the FTP Sensor section in Circuit/System Testing. |
- Install the fuel cap.
- 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 12 inches H2O.
⇒ | If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing. |
- 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
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 12 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. |
FTP Sensor
- Ignition OFF, disconnect the harness connector at the FTP sensor.
- Ignition OFF, test for less than 5 ohms between the low reference circuit terminal 2 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 FTP sensor. |
Repair Instructions
Repair Verification
Note: Larger volume fuel tanks and/or those with lower fuel levels may require several minutes for the floating indicator to stabilize.
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 8 inches H2O.