The evaporative emission (EVAP) system is used to store fuel vapors as to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, fuel tank pressure sensor, EVAP lines and hoses, EVAP purge solenoid - normally closed, EVAP service port, EVAP vent solenoid - normally open, fuel tank and powertrain control module (PCM). The PCM monitors the EVAP system for circuit faults in the fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. The PCM also monitors the EVAP system for small and large leaks. During DTC P0446 diagnostic, the EVAP purge solenoid is commanded ON, open, and the EVAP vent solenoid is commanded ON, closed, in order to build vacuum. Once vacuum is obtained, the EVAP vent solenoid is commanded OFF and the vacuum should decrease rapidly. DTC P0446 sets when the vacuum does not decay indicating a blocked vent system.
DTC Parameters
DTC P0446 will set if EVAP system has reached 12 inches of H2O or greater for longer than 1.6 seconds indicating a blocked vent system when:
| • | 9 inches of H2O initially pulled on the fuel tank. |
| • | The EVAP purge solenoid is commanded ON, fixed pulse width modulation (PWM). |
| • | The EVAP vent solenoid is commanded OFF, open. |
| • | The engine run time is less than 2 minutes and 24 seconds. |
| • | The fuel level is between 15-85 percent full. |
| • | The barometric (BARO) is greater than 81 kPa. |
| • | The ignition voltage is between 11-18 volts. |
| • | The engine coolant temperature (ECT) and intake air temperature (IAT) at engine startup are between 5-32°C (41-90°F). |
| • | The ECT and IAT are within 10°C (50°F) of each other |
| • | No ECT, fuel tank pressure, IAT, manifold absolute pressure (MAP) or vehicle speed DTCs have been set. |
DTC P0446 diagnostic is run once during the EVAP diagnostic test for a maximum of 96 seconds once the above conditions have been met.
DTC P0446 diagnostic may also run during initial key-up. The diagnostic runs at this time only when strict operating parameters have been met. Under most conditions, the test will run during the regular EVAP diagnostic test.
DTC P0446 is a type A DTC.
Diagnostic Aids
Important: If DTC P0447 is set, diagnose that DTC first. A short to ground causing the EVAP vent solenoid ON, will cause the vent valve to close. This will cause DTC P0446 to set.
Important: The PCM uses the fuel tank pressure sensor to detect the vacuum decay of the EVAP vent solenoid diagnostic. Make sure the fuel pressure sensor is not skewed by verifying the FUEL TANK PRESS. SENSOR on a scan tool is between 1.3-1.7 volts with the ignition ON and the fuel cap removed.
Check the following for causes of a blocked vent system:
| • | The EVAP vent solenoid blocked or stuck valve |
| • | The vent hose plugged, kinked or pinched |
| • | The EVAP canister restricted |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Is DTC P0447 set ? | -- | Go to DTC P0447 | Go to Step 2 | |||||||
2 | Inspect the evaporative emission (EVAP) system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 3 | ||||||
3 |
Is the Fuel Tank Pressure 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.
Does the Fuel Tank Pressure sensor parameter closely match the gage reading on the EEST? | 5 in H2O | Go to Step 5 | Go to Step 8 | ||||||
5 | Command the EVAP vent solenoid open with a scan tool. Is the Fuel Tank Pressure Sensor parameter less than the specified value? | 1 in H2O | Go to Diagnostic Aids | Go to Step 6 | ||||||
6 | Remove the EVAP canister vent solenoid from the EVAP canister. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Is the Fuel Tank Pressure Sensor parameter less than the specified value ? | 1 in H2O | Go to Step 10 | Go to Step 7 | ||||||
7 | Disconnect the EVAP vent hose from the EVAP canister. Is the Fuel Tank Pressure Sensor parameter less than the specified value? | 1 in H2O | Go to Step 11 | Go to Step 9 | ||||||
8 | Test for an intermittent and for a poor connection at the fuel tank pressure (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 13 | Go to Step 12 | ||||||
9 | Repair the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 13 | -- | ||||||
10 | Replace the EVAP vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
11 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
12 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
13 |
Important: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
Is the Fuel Tank Pressure Sensor parameter less than the second specified value within 60 seconds. | 5 in H2O 1 in H2O | Go to Step 14 | Go to Step 1 | ||||||
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 | System OK |
