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
| • | Before the ECM can report DTC P0446 failed, DTCs P0442 and P0496 must run and pass. |
| • | DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0443, P0449, P0451, P0453, P0454, 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 between 4-30°C (39-86°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 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
| • | The control module illuminates the malfunction indicator lamp
(MIL) on the second consecutive ignition cycle that the diagnostic runs and
fails. |
| • | The control module records the operating conditions at the time
the diagnostic fails. The first time the diagnostic fails, the control module
stores this information in the Failure Records. If the diagnostic reports
a failure on the second consecutive ignition cycle, the control module
records the operating conditions at the time of the failure. The control
module writes the operating conditions to the Freeze Frame and updates
the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL)
after 3 consecutive ignition cycles that the diagnostic runs and does
not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs
and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles,
if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
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 5 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
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.
