System Description
This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid Open and the EVAP canister vent solenoid Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid Closed and the EVAP canister vent solenoid Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, this DTC sets.
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.
Control Module Command | EVAP Canister Purge Solenoid | EVAP Canister Vent Solenoid |
|---|---|---|
ON | Open | Closed |
OFF | Closed | Open |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0446 Evaporative Emission (EVAP) Vent System Performance
Conditions for Running the DTC
| • | Before the ECM can report DTC P0446 failed, DTCs P0451, P0452, and P0453 must run and pass. |
| • | DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0221, P0222, P0223, P0443, P0449, P0458, P0459, P0496, P0498, P0499, P0560, P0562, P0563, P0722, P0723, P2122, P2123, P2127, P2128 and P2138 are not set. |
| • | The ignition 1 voltage is more than 10.5 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The engine run time is more than 10 minutes or the fuel trim is stable. |
| • | The engine is idling. |
| • | The FTP is between -18.7 and +7.5 mm Hg (-10.0 and +4.0 in. H2O). |
| • | The ambient air temperature (AAT) is between 2-32°C (35-90°F). |
| • | The ECT and the AAT are within 10°C (18°F) of each other at engine start-up. |
| • | The fuel level is between 12-88 percent. |
| • | The vehicle speed sensor (VSS) is less than 2 km/h (3 mph). |
| • | The above conditions exist for more than 5 seconds. |
| • | DTC P0446 will attempt to run up to 10 times or the test completes successfully once per ignition cycle. |
Conditions for Setting the DTC
| • | The FTP is less than -6.0 mm Hg (-3.2 in. H2O). |
| • | The condition is present for more than 4 seconds. |
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 4 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 vent valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill condition.
Test Description
The number below refers to the step number on the diagnostic table.
-
This step determines if a condition exists with the FTP sensor. The FTP sensor parameter should display near zero inches of H2O with the fuel fill cap removed and the EVAP purge hose disconnected from the EVAP purge solenoid. Higher ambient air temperatures, or vehicle under-body temperatures could cause a higher than normal FTP reading. Allow the vehicle and/or the air surrounding the fuel tank to cool before proceeding with this step.
-
The EVAP vent solenoid valve is located inside the EVAP canister. The EVAP canister must be removed from the vehicle to access the EVAP vent solenoid valve. Once the EVAP solenoid vent valve has been removed from the EVAP canister, the electrical connector is re-connected. The vent solenoid valve is observed while being commanded ON and OFF with a scan tool.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Evaporative Emissions Hose Routing Diagram | ||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||
2 | Inspect the evaporative emission (EVAP) system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 3 | ||||||
|
Important: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure.
Is the Fuel Tank Pressure sensor parameter within the specified range? | -1 and +1 in H2O | Go to Step 4 | Go to Step 6 | |||||||
Important: The DTCs may need to be cleared if the output control does not operate. Does the EVAP vent valve open and close? | -- | Go to Step 5 | Go to Step 7 | |||||||
5 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | ||||||
6 | Test for an intermittent and for a poor connection at the fuel tank pressure (FTP) sensor and at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||
7 | Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||
8 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||
9 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||
10 |
Important: Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Important: The DTCs may need to be cleared if the output control does not operate. Is the Fuel Tank Pressure sensor parameter less than the second parameter? | 5 in H2O 1 in H2O | Go to Step 11 | Go to Step 2 | ||||||
11 |
Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
