System Description
When running the DTC P0446 Evaporative Emission (EVAP) Vent System Performance diagnostic, the powertrain control module (PCM ), monitors the fuel tank pressure (FTP) sensor. When vapor pressure rises to a specified value, the PCM commands the vent valve open, and monitors the FTP sensor signal. Pressure will increase rapidly because of the air allowed into the system. No increase or an increase below a specified rate indicates a restriction on the air inlet side. The PCM then commands the pressure switching solenoid closed. This blocks air from entering the tank side of the system. The PCM monitors the fuel tank pressure FTP sensor and looks for a decrease in the pressure rise. If there is no change in pressure the PCM concludes the pressure switching solenoid did not close. If the PCM does not detect an increase in pressure, or the rise in pressure does not change, a DTC P0446 will set.
Conditions for Running the DTC
| • | The barometric pressure (BARO) is more than 75 kPa. |
| • | The fuel level is between 25-75 percent. |
| • | The ECT sensor and the intake air temperature (IAT) sensor are near the same temperature at engine start. |
| • | The ECT sensor is at least 74°C (165°F) after engine warm up. |
Conditions for Setting the DTC
The pressure indicated in the EVAP canister and the fuel tank does not drop when the EVAP canister purge valve is ON.
OR:
The pressure indicated in the EVAP canister remains very low when compared to atmospheric pressure when the EVAP canister purge solenoid valve is OFF.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear Information function. |
Diagnostic Aids
| • | If DTC P0446 is the only EVAP DTC set, the most likely cause is an inoperable EVAP canister vent solenoid, or pressure switching solenoid. Inspect the EVAP solenoids carefully for faulty connections and erratic operation. |
| • | An intermittent malfunction may be caused by a fault in any of the EVAP solenoid electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to . |
| • | If the DTC cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set. |
| • | Operating the vehicle in Check Mode will increase the ability of the powertrain control (PCM) module to detect engine control system malfunctions. Refer to Check Mode in Service Bay Test . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the DTC P0446 is captured in the freeze frame/failure record list. When multiple EVAP system DTCs are set, the DTC stored in the freeze frame/failure record is the best diagnostic starting point.
-
This step uses the EVAP Purge/Seal function to test for the correct operation of the EVAP canister vent solenoid, the pressure switching solenoid, and the purge solenoid. Using the EVAP Purge/Seal function also tests for leaks by allowing the technician to seal the system and monitor the FTP sensor.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics and Evaporative Emissions Hose Routing Diagram Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Install a scan tool and check for DTCs. Is a DTC P0450. P0451, P0452, or P0453 present? | -- | Go to Scan Tool Data List | Go to Step 3 |
Is DTC P0446 captured in the Freeze Frame/Failure records? | -- | Go to Step 4 | ||
4 | Command the EVAP vent solenoid ON and OFF with the scan tool. Refer to Scan Tool Output Controls . Do you hear or feel a click as the EVAP vent solenoid is commanded ON and OFF? | -- | Go to Step 5 | Go to Step 11 |
5 | Command the EVAP pressure switching solenoid ON and OFF with the scan tool. Do you hear or feel a click as the EVAP pressure switching solenoid is commanded ON and OFF? | -- | Go to Step 6 | Go to Step 13 |
6 |
Is the FTP sensor within the specified range? | 0.17 mm Hg (0.09 in H2O) | Go to Step 7 | Go to Step 20 |
7 |
Did you achieve a vacuum? | -- | Go to Step 8 | Go to Step 22 |
8 | Command the EVAP vent solenoid OFF, open. Does the vacuum decrease? | -- | Go to Step 9 | Go to Step 23 |
9 |
Did you achieve a vacuum? | -- | Go to Step 10 | Go to Step 25 |
10 | Command the EVAP pressure switching ON , open. Does the vacuum decrease? | -- | Go to Step 28 | Go to Step 25 |
11 |
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 17 |
12 |
Does the test lamp illuminate when the EVAP vent solenoid is commanded ON and turn OFF when the EVAP vent solenoid is commanded OFF? | -- | Go to Step 18 | Go to Step 15 |
13 |
Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 17 |
14 |
Does the test lamp illuminate when the EVAP pressure switching solenoid is commanded ON and turn OFF when the EVAP pressure switching solenoid is commanded OFF? | -- | Go to Step 19 | Go to Step 16 |
15 | Test the control circuit of the EVAP vent solenoid for an open, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 21 |
16 | Test the control circuit of the EVAP pressure switching solenoid for an open, a short to ground, or for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 21 |
17 |
Did you complete the repair? | -- | Go to Step 28 | -- |
18 | Test for an intermittent and for a poor connection at the EVAP canister vent solenoid. 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 28 | Go to Step 24 |
19 | Test for an intermittent and for a poor connection at the EVAP pressure switching solenoid. 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 28 | Go to Step 25 |
20 | 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 in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 26 |
21 | Test for an intermittent and for a poor connection at the control module. 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 28 | Go to Step 27 |
22 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
23 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
24 | Replace the EVAP vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 28 | -- |
25 | Replace the EVAP pressure switching solenoid. Refer to Evaporative Emission Pressure Switching Solenoid Replacement . Did you complete the replacement? | -- | Go to Step 28 | -- |
26 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 28 | -- |
27 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 28 | -- |
Does the FTP sensor indicate a reading of at least the first specified value for as long as the second specified value? | -28.20 mm Hg (-15.10 in H2O) 2 minutes | Go to Step 29 | Go to Step 4 | |
29 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
