Description
A restricted or blocked evaporative emission (EVAP) vent path is detected by the powertrain control module (PCM) commanding the purge valve ON (open) and the vent valve ON (closed) allowing a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the PCM commands the purge valve OFF (closed) and the vent valve OFF (open) while monitoring the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches of H2O in a calibrated time, DTC P0446 will set.
Conditions for Running the DTC
| • | DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0452, or P0453 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 121 km/h (75 mph). |
Conditions for Setting the DTC
| • | Fuel tank pressure is less than -10 inches of 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) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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
The EVAP system tests run when the engine is first started and meets the Conditions for Running the DTC. 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 problem. To repair a blockage in the EVAP system, refer to Evaporative Emission System Cleaning .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step checks if the FTP sensor is functioning.
-
This step checks if the condition is present.
-
This step checks the EVAP vent valve electrical operation.
-
This step checks for a restricted EVAP vent valve
-
This step checks if the restriction is in the EVAP canister or the vent hose.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics and Emission Hose Routing Diagram | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 | Did DTCs P0452 or P0453 also set? | -- | Go to Step 3 | |||||
3 | Inspect the EVAP system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 4 | ||||
Are the EVAP pressure/purge diagnostic station gauge and the scan tool FTP sensor values similar? | 13 in. H2O | Go to Step 5 | Go to Step 9 | |||||
Did the EVAP pressure/purge diagnostic station gauge drop quickly to near the specified value? | 0 in. H2O | Go to Intermittent Conditions | Go to Step 6 | |||||
Command the EVAP vent valve ON and OFF with a scan tool. Does the EVAP vent valve click when commanded ON and OFF? | -- | Go to Step 7 | Go to Step 10 | |||||
Does the scan tool indicate fuel tank pressure near the second specified value? | 13 in. H2O 0 in H2O | Go to Step 14 | Go to Step 8 | |||||
Disconnect the EVAP vent hose from the EVAP canister. Does the scan tool indicate fuel tank pressure near the specified value? | 0 in. H2O | Go to Step 16 | Go to Step 15 | |||||
9 | Is the FTP sensor value more than the specified value? | 4.3 V | Go to DTC P0453 | Go to Step 12 | ||||
10 |
Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 14 | ||||
11 | Test the control circuit of the EVAP vent valve for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 13 | ||||
12 | Test for poor connections at the harness connector of the FTP. 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 19 | Go to Step 17 | ||||
13 | Test for poor connections at the harness connector of the PCM. 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 19 | Go to Step 18 | ||||
14 | Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||
15 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||
16 | Repair the blockage in the EVAP vent hose. Did you complete the repair? | -- | Go to Step 19 | -- | ||||
17 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||
18 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||
19 |
Is the EVAP Pressure/Purge Diagnostic Station valve near the second specified value? | 13 in. H2O 0 in. H2O | Go to Step 20 | Go to Step 3 | ||||
20 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
