| 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
| • | DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0221, P0222, P0223, P0451, P0452, P0453, P0496, P0560, P0562, and P0563 are not set. |
| • | The ignition 1 voltage is more than 10 volts. |
| • | The fuel system is operating in closed loop. |
| • | The engine is idling. |
| • | The volumetric efficiency is less than 35 percent. |
| • | The barometric pressure (BARO) is more than 68 kPa. |
| • | The fuel level is between 15-85 percent. |
| • | The engine coolant temperature (ECT) is between 4-65°C (39-149°F). |
| • | The intake air temperature (IAT) is between 4-30°C (39-86°F). |
| • | The vehicle speed sensor (VSS) is less than 2 km/h (3 mph). |
Conditions for Setting the DTC
| • | The FTP is less than -1 inch H2O. |
| • | The engine control module (ECM) detects a large leak in the EVAP system. |
| • | The condition is present for more than 5 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 numbers below refer to the step numbers on the diagnostic table.
-
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-Engine Controls? | -- | 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 | ||||||||
3 |
Is the Fuel Tank Pressure sensor parameter within the specified range? | -1 and +1 in H20 | Go to Step 4 | Go to Step 8 | ||||||||
Important:
Does the EVAP vent valve open and close? | -- | Go to Step 5 | Go to Step 6 | |||||||||
5 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 | ||||||||
6 | Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
7 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
8 | Replace the fuel tank pressure (FTP) sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
9 |
Important: Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Important:
Important:
Is the Fuel Tank Pressure sensor parameter less than the second parameter? | 5 in H2O 1 in H2O | Go to Step 10 | Go to Step 2 | ||||||||
10 |
Are there any DTCs that have not been diagnosed? | System OK | ||||||||||
