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 EVAP Vent System Performance
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0139, P0140, P0141, P0150, P0151, P0152, P0153, P0154, P0155, P0156, P0157, P0158, P0159, P0160, P0161, P0221, P0222, P0223, P0442, P0443, P0449, P0451, P0452, P0453, P0455, P0458, P0459, P0498, P0499, P0506, P0507, P1271, P1277, P1278, P1282, P1283, P1511, P1516, P1519, P1523, P1526, P1530, P1551, P2100, P2101, P2107, P2119, P2122, P2123, P2127, P2128, P2138, P2176 are not set. |
| • | The EVAP canister purge solenoid valve is commanded to a constant duty cycle. |
| • | The EVAP canister vent solenoid valve is commanded OFF. |
| • | The engine is at idle. |
| • | The vehicle speed is 0 km/h (0 mph). |
| • | The engine load is less than 35 percent. |
| • | The manifold absolute pressure (MAP) is less than 40 kPa. |
| • | The battery voltage is greater than 10.5 volts. |
| • | The engine coolant temperature (ECT) at engine start-up is between 8-75°C (46-167°F). |
| • | The intake air temperature (IAT) is between 8-75°C (46-167°F). |
| • | Fuel level is between 6-48 liters (1.6-12.7 gallons). |
| • | DTC P0446 diagnostic runs once per ignition cycle. |
Conditions for Setting the DTC
The FTP sensor voltage is less than a calibrated amount within a calibrated amount of time.
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 DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | If DTC P0442, P0446, or P0455 is set, EVAP special functions on the scan tool will not be allowed. Clear DTCs before performing these tests. |
| • | The engine control module (ECM) uses the FTP sensor to detect the vapor in the fuel tank during all parts of the EVAP diagnostic system test. Make sure the FTP sensor is not skewed by verifying FTP SENSOR on the scan tool is between 2.35-2.85 volts with the ignition ON and the engine OFF. |
| • | Possible causes of a blocked EVAP vent system: |
| - | The EVAP vent solenoid valve has a blocked or stuck valve. |
| - | The EVAP vent hose from the EVAP canister to the EVAP vent line or the EVAP hose at the EVAP vent box is kinked or pinched. |
| - | The EVAP canister is restricted. |
| - | An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP 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 Intermittent Conditions . |
| - | If an EVAP diagnostic test is aborted due to changing enabled criteria, the ECM will run the entire EVAP test up to 3 times per ignition cycle. |
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 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||
2 | Inspect the evaporative emission (EVAP) system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 3 | ||||||
3 |
Is the fuel tank pressure (FTP) sensor parameter within the specified range? | -1 to +1 in H2O | Go to Step 4 | Go to Step 8 | ||||||
4 |
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 5 | ||||||
5 | 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 10 | Go to Step 6 | ||||||
6 | 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 7 | Go to Step 11 | ||||||
7 | Repair the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 12 | -- | ||||||
8 | Test for poor connections at the harness connector of the FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||
9 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
10 | Replace the EVAP canister vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
11 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
12 |
Is the FTP sensor parameter within the specified range? | -1 to +1 in H2O | Go to Step 13 | Go to Step 2 | ||||||
13 |
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 Step 14 | Go to Step 2 | ||||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||
