| Table 1: | DTC P0446 Evaporative Emission (EVAP) Vent System Performance |
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 engine control module (ECM) can report DTC P0446 failed, DTC 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, P0451, P0452, P0453, P0458, P0459, P0496, P0498, P0499, P0560, P0562, P0563, P0700, P2122, P2123, P2127, P2128, and P2138, are not set. |
| • | The ignition 1 voltage is between 10.5-18 volts. |
| • | The fuel system is operating in closed loop. |
| • | The engine is idling. |
| • | The ambient air temperature is between 2-32°C (36-90°F). |
| • | The start-up engine coolant temperature (ECT) is within 10°C (18°F) of ambient air temperature. |
| • | The FTP is between -1.8 to +7.5 mm Hg (-1.0 to +4.0 in H2O). |
| • | The volumetric efficiency is less than 35 percent. |
| • | The barometric pressure (BARO) is more than 68 kPa. |
| • | The fuel level is between 12-88 percent. |
| • | The vehicle speed sensor (VSS) is less than 2 km/h (3 mph). |
| • | The engine is operating for more than 16 minutes or the long term fuel trim is stable. |
| • | The conditions above 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 -2.0 mm Hg (-1 in H2O). |
| • | The ECM detects a large leak in the EVAP system. |
| • | 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
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This step tests the operation of the FTP sensor. If the FTP parameter is more or less than an atmospheric value when the purge hose is disconnected from the purge solenoid, replace the FTP sensor.
-
This step tests for a restriction in the EVAP vent system. If the FTP sensor parameter does not return to the second value there is a restriction in the vent system.
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 9 | 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 H20 | Go to Step 4 | Go to Step 7 | |||||
|
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 specified value? | 5 in H2O 1 in H2O | Go to Diagnostic Aids | Go to Step 5 | |||||
5 | Disconnect the EVAP vent hose from the EVAP vent valve solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Is the Fuel Tank Pressure sensor parameter less than the specified value? | 1 in H2O | Go to Step 9 | Go to Step 6 | ||||
6 | Disconnect the EVAP vent hose from the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the Fuel Tank Pressure sensor parameter less than the specified value? | 1 in H2O | Go to Step 8 | Go to Step 10 | ||||
7 | Test for an intermittent and for a poor connection at the fuel tank pressure (FTP) 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 12 | Go to Step 11 | ||||
8 | Repair the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 12 | -- | ||||
9 | Replace the EVAP vent valve solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
10 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
11 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
12 |
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. 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 13 | Go to Step 2 | ||||
13 |
Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
