System Description
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 (FTP) sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open) and fuel tank. The engine control module (ECM) monitors the EVAP system for circuit faults in the EVAP purge solenoid, EVAP vent and purge solenoid). When certain conditions have been met, the ECM will perform an EVAP diagnostic test at idle with no vehicle speed. DTC P0446 will set if too much vacuum is present with the EVAP vent solenoid commanded OFF during the EVAP diagnostic system test indicating a blocked EVAP vent system.
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0139, P0140, P0141, P0150, P0151, P0152, P0153, P0154, P0155, P0156, P0157, P0158, P0159, P0160, P0161, P0221, P0222, P0223, P0442, P0443, P0444, P0445, P0447, P0448, P0449, P0451, P0452, P0453, P0455, P0506, P0507, P1271, P1277, P1278, P1282, P1283, P1511, P1516, P1519, P1523, P1526, P1530, P1551, P2100, P2101, P2107, P2119, P2122, P2123, P2127, P2128, P2138, P2176 are not set. |
| • | The EVAP purge solenoid is commanded to a certain duty cycle. |
| • | The EVAP vent solenoid is commanded OFF. |
| • | The engine is at idle. |
| • | The engine load is less than 35 percent. |
| • | The manifold absolute pressure (MAP) is less than 40 kPa. |
| • | The battery voltage is greater than 11 volts. |
| • | The engine coolant temperature (ECT) at engine startup is between 8-75°C (46-167°F). |
| • | The intake air temperature (IAT) is between 8-75°C (46-167°F). |
| • | The long term FT cells learned (if not learned, engine must run longer than 16 minutes and 45 seconds). |
| • | Fuel level is between 6-48 L (1.6-12.7 gallons). |
DTC P0446 diagnostic runs once per ignition cycle.
Conditions for Setting the DTC
The FTP sensor is less than a calibrated amount within a calibrated amount of time.
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 DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | If DTC P0440, P0442, P0446 or P0455 is set, EVAP special functions on the scan tool will not be allowed. Clear DTCs before performing these tests. |
| • | The ECM uses the FTP sensor to detect the vapor in the fuel tank during all parts of the EVAP diagnostic system test. Make sure the FTP sensor is not skewed by verifying FTP SENSOR on the scan tool is between 2.35 and 2.85 volts with the ignition ON and the engine OFF. |
| • | Possible causes of a blocked EVAP vent system: |
| - | The EVAP vent solenoid has a blocked or stuck valve. |
| - | The EVAP vent hose from the EVAP canister to the EVAP vent line or the EVAP hose at the EVAP vent box is kinked or pinched. |
| - | The EVAP canister is restricted. |
| - | An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent solenoid inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem. |
| - | For intermittent conditions refer to Intermittent Conditions . |
| - | If an EVAP diagnostic test is aborted due to changing enabled criteria, the ECM will run the entire EVAP test up to 3 times per ignition cycle. |
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 |
Does the scan tool indicate that the Service Bay Test passed? | -- | Go to Diagnostic Aids | Go to Step 3 | ||||||
3 | Inspect the evaporative emission EVAP system for the following conditions:
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 4 | ||||||
4 |
Is the fuel tank pressure (FTP) Sensor parameter within the specified range? | -1 to + 1 in H2O | Go to Step 5 | Go to Step 9 | ||||||
5 |
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? | 5 in H2O 1 in H2O | Go to Diagnostic Aids | Go to Step 6 | ||||||
6 | Disconnect the EVAP vent hose from the EVAP vent solenoid. Is the FTP Sensor parameter less than the specified value? | 1 in H2O | Go to Step 11 | Go to Step 7 | ||||||
7 | Disconnect the EVAP vent hose from the EVAP canister. Is the FTP Sensor parameter less than the specified value? | 1 in H2O | Go to Step 8 | Go to Step 12 | ||||||
8 | Repair or replace the pinched or restricted EVAP vent hose. Did you complete the repair? | -- | Go to Step 13 | -- | ||||||
9 | 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 13 | Go to Step 10 | ||||||
10 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
11 | Replace the EVAP vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
12 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
13 | Perform the Service Bay Test. Refer to Service Bay Test . Does the scan tool indicate that the Service Bay Test passed? | -- | Go to Step 14 | Go to Step 3 | ||||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
