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. |
Conditions for Setting the DTC
| • | The FTP sensor is greater than 10 inches H2O. |
| • | The condition is present for as long as 30 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 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
| Important: DO NOT use more than 5 in H2O. More than 5 in 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. |
| • | When using the electronic 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. |
| • | 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 condition. |
| • | An EVAP canister valve, a vent hose valve, or a vent solenoid valve that has restricted flow may cause this DTC to set. Using the purge solenoid valve command with a scan tool will allow vacuum to be applied to the system instead of pressure. With the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 percent, vacuum should not increase to more then 9 inches H2O. |
| • | For intermittent conditions, refer to Intermittent Conditions . |
Test Description
The number below refers to the step number on the diagnostic table.
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 |
Does the scan tool indicate that the Service Bay Test passed? | -- | Go to Diagnostic Aids | Go to Step 3 | ||||||
3 | Inspect the evaporative emission (EVAP) system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 4 | ||||||
Is the fuel tank pressure (FTP) sensor parameter within the specified range? | -1 to +1 in H20 | Go to Step 5 | Go to Step 9 | |||||||
5 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Is the FTP sensor parameter less than the second specified value? | 5 in H2O 1 in H2O | Go to Diagnostic Aids | Go to Step 6 | ||||||
6 | Disconnect the EVAP vent hose from the EVAP canister vent solenoid valve. Is the FTP sensor parameter less than the specified value? | 1 in H2O | Go to Step 12 | Go to Step 7 | ||||||
7 | Disconnect the EVAP vent hose from the EVAP canister. Is the FTP sensor parameter less than the specified value? | 1 in H2O | Go to Step 8 | Go to Step 13 | ||||||
8 | Repair the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||
9 | Test for an intermittent and for a poor connection at the FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 | ||||||
10 | Test the low reference circuit of the FTP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
11 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
12 | Replace the EVAP canister vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
13 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
14 | Perform the Service Bay Test. Refer to Service Bay Test . Does the scan tool indicate that the Service Bay Test passed? | -- | Go to Step 15 | Go to Step 3 | ||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
