Circuit 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 will set.
DTC Descriptors
This diagnostic procedure supports the following DTC.
DTC P0446 Evaporative Emissions (EVAP) Vent System Performance
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0171, P0172, P0174, P0175, P0452, P0453, P0502, P0503, P0641, P0651, P1111, P1112, P1114, P1115, P1121, P1122, P1133, P1134, P1153, and P1154 are not set. |
| • | The system voltage is between 10-18 volts. |
| • | The startup ECT is between 4-30°C (39-86°F). |
| • | The startup IAT is between 4-30°C (39-86°F). |
| • | The start up ECT and IAT are within 8°C (14°F) of each other. |
| • | The fuel tank level is between 15-85 percent. |
| • | The startup barometric pressure (BARO) is more than 75 kPa. |
| • | The vehicle speed sensor (VSS) is less than 90 km/h (75 mph). |
| • | DTC P0446 runs once per ignition cycle when the above conditions are met. |
Conditions for Setting the DTC
Condition 1
| • | Fuel tank pressure is more than 16.8 mm Hg (9 inch H2O) when the vent solenoid is OPEN during normal EVAP purging. |
| • | The above condition is present for at least 23 seconds. |
Condition 2
| • | Fuel tank pressure is more than 9.3 mm Hg (5 inch H2O) or less than -4.7 mm Hg (-2.5 inch H2O) at cold engine startup. |
| • | The above condition is present for at least 3 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
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: Engine Controls Schematics 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 | Did DTC P0443, P0449, P0452 or P0453 set? | -- | Go to Step 3 | |||||||
3 | Inspect the EVAP system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 4 | ||||||
Does the scan tool indicate that the Service Bay Test has passed? | -- | Go to Diagnostic Aids | Go to Step 5 | |||||||
5 |
Does the scan tool indicate fuel tank pressure near the specified value? | 0 in H2O | Go to Step 6 | Go to Step 9 | ||||||
6 |
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 7 | ||||||
7 | 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 11 | Go to Step 8 | ||||||
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 14 | Go to Step 12 | ||||||
9 | 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 10 | ||||||
10 | 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 15 | Go to Step 13 | ||||||
11 | Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
12 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
13 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
14 | Repair for a blockage in the EVAP vent hose. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||
15 |
Does the scan tool indicate that the Service Bay Test has passed? | -- | Go to Step 16 | Go to Step 3 | ||||||
16 | With a scan tool, select the Review Info option. Does the scan tool indicate any DTCs that have not been diagnosed? | -- | System OK | |||||||
