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 valve Open and the EVAP canister vent solenoid valve 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 valve Closed and the EVAP canister vent solenoid valve 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 solenoid valves.
Control Module Command | EVAP Canister Purge Solenoid Valve | EVAP Canister Vent Solenoid Valve |
|---|---|---|
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 PCM can report DTC P0446 failed, DTCs P0442 and P0496 must run and pass. |
| • | DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0125, P0128, P0443, P0449, P0451, P0452, P0453, P0455, P0502, 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 75 kPa. |
| • | The fuel level is between 15-85 percent. |
| • | The engine coolant temperature (ECT) is between 4-30°C (39-86°F). |
| • | The 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. |
| • | The vehicle speed sensor (VSS) is less than 129 km/h (80 mph). |
| • | DTC P0446 runs once per cold start when the above conditions are met. |
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
| • | When using the Evaporative Emission System Tester (EEST) to apply pressure, you can regulate the amount of pressure by activating the remote switch on and off while observing pressure in the EVAP system using a scan tool. DO NOT use more than 5 inches H2O. More than 5 inches H2O applied to the EVAP system can cause the canister vent solenoid valve to temporarily remain in the closed position, which could lead to misdiagnosis in this procedure. |
| • | 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. |
| • | For intermittent conditions, refer to Testing for Intermittent Conditions and Poor Connections . |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
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 13 | Go to Step 3 | ||||||
Is the fuel tank pressure sensor parameter within the specified range? | -1 to +1 in H2O | Go to Step 4 | Go to Step 7 | |||||||
4 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
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 canister vent solenoid valve. Is the fuel tank pressure sensor parameter less than the specified value? | 1 in H2O | Go to Step 11 | Go to Step 6 | ||||||
6 | Disconnect the EVAP vent hose from the EVAP canister. Is the fuel tank pressure sensor parameter less than the specified value? | 1 in H2O | Go to Step 9 | Go to Step 12 | ||||||
7 | Test for poor connections at the harness connector of the fuel tank pressure (FTP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8 | ||||||
8 | Test the low reference circuit of the FTP sensor for a high resistance or an open. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||
9 | Repair the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 13 | -- | ||||||
10 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
11 | Replace the EVAP canister vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
12 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
13 |
Is the fuel tank pressure sensor parameter within the specified range? | -1 to + 1 in H2O | Go to Step 14 | Go to Step 2 | ||||||
14 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Is the fuel tank pressure sensor parameter less than the second specified value? | 5 in H2O 1 in H2O | Go to Step 15 | Go to Step 2 | ||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
