System Description
A restricted or blocked evaporative emission (EVAP) vent path is detected by the control module 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 control module 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 H2O in a calibrated time, DTC P0446 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 valves.
Control Module Command | EVAP Canister Purge Valve | EVAP Canister Vent Valve |
|---|---|---|
ON | Open | Closed |
OFF | Closed | Open |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0446 Evaporative Emissions (EVAP) Vent System Performance
Conditions for Running the DTC
| • | Before the engine control module (ECM) can report DTC P0446 failed, DTCs P0442, P0456, and P0496 must run and pass. |
| • | DTCs P0106, P0107, P0108, P112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0300, P0402, P0404, P0405, P0406, P0443, P0452, P0453, P0462, P0463, P0488, P0502, P0506, P0507, P2195, and P2196 are not set. |
| • | The ignition 1 voltage is between 11-16 volts. |
| • | The barometric pressure (BARO) is more than 72 kPa. |
| • | The engine coolant temperature (ECT) and the intake air temperature (IAT) at start-up are between -5°C and +40°C (+23°F and +140°F). |
| • | The purge enable time is less than 360 seconds. |
| • | The fuel level is between 24-94 percent. |
| • | The start-up IAT minus the start-up ECT is within 12°C (22°F). |
| • | The start-up ECT minus start-up IAT is within 50°C (90°F). |
| • | DTC P0446 runs once an ignition cycle when the above conditions are met. |
Conditions for Setting the DTC
| • | The ECM detects that the fuel tank pressure is more than 9.3 mm Hg (5 inches H2O) or less than -4.7 mm Hg (-2.5 inches H2O) at cold engine startup. |
| • | The above condition is present for at least 2 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
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.
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 - Engine Controls? | -- | Go to Step 2 | |||||
2 | Did DTC P0443, P0449, P0452 or P0453 set? | -- | Go to Step 3 | |||||
3 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 4 | ||||
Does the scan tool indicate fuel tank pressure near the specified value? | 0 in H2O | Go to Step 5 | Go to Step 8 | |||||
5 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Does the scan tool indicate fuel tank pressure near the second specified value? | 5 in H2O 0 in H2O | Go to Diagnostic Aids | Go to Step 6 | ||||
6 | Disconnect the EVAP vent hose from the EVAP vent valve. Does the scan tool indicate fuel tank pressure near the specified value? | 0 in H2O | Go to Step 10 | Go to Step 7 | ||||
7 | 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 13 | Go to Step 11 | ||||
8 | With a scan tool, observe the fuel tank pressure sensor voltage. Is the FTP sensor voltage more than the specified value? | 4.3 V | Go to DTC P0453 | Go to Step 9 | ||||
9 | Test for poor connections at the harness of the fuel tank pressure 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 14 | Go to Step 12 | ||||
10 | Replace the EVAP vent valve. Did you complete the replacement? | -- | Go to Step 14 | -- | ||||
11 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||
12 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||
13 | Repair for a blockage in the EVAP vent hose. Did you complete the repair? | -- | Go to Step 14 | -- | ||||
14 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Does the scan tool indicate fuel tank pressure near the second specified value? | 5 in H2O 0 in H2O | 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 | |||||
