Circuit Description
The DTC P0449 Evaporative Emission (EVAP) Vent System Performance diagnostic monitors the control circuit voltage of the EVAP vent valve. Ignition voltage is supplied directly to the EVAP vent valve solenoid. The powertrain control module (PCM) supplies a ground path to the solenoid control circuit using an internal solid state device called a driver. Each driver has a fault line that is monitored by the PCM. When the PCM commands the solenoid ON, the voltage on the control circuit should be near zero or low. When the PCM commands the solenoid OFF, the voltage on the control circuit should be near battery voltage or high. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.
The PCM will monitor the solenoid control circuit for the following conditions:
| • | A short to ground |
| • | A short to voltage |
| • | An open circuit |
| • | An open solenoid |
| • | An internally shorted or excessively low resistance solenoid coil |
Condition for Running the DTC
| • | Ignition is ON or the engine is running. |
| • | Intake Air Temperature (IAT) is greater than -8°C (18°F). |
| • | Engine Coolant Temperature (ECT) is between -8 and 110°C (18 and 230°F). |
Conditions for Setting the DTC
The PCM does not detect the expected voltage on the EVAP vent valve control circuit.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A history DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
Test the operation of the EVAP canister vent valve. Refer to Evaporative Emission Control System Diagnosis .
If a DTC P0449 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Evaporative Emission System Set .
An intermittent malfunction may be caused by a fault in the electrical circuit of the EVAP vent valve . Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0449 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step determines if the condition that caused DTC P0449 to set still exists.
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This step checks the control circuit of the EVAP vent valve . The duty cycle control of the EVAP vent valve is disabled by the PCM until the engine has reached a normal operating temperature of at least 80°C (176°F), there is no RPM indicated, and there are no DTCs set. The output controls can be found on the scan tool under Special Functions.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0449 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0449 appears in the Not Ran Since Code Cleared list, the DTC P0449 diagnostic has not yet run. When the DTC P0449 does not appear in the Not Ran Since Code Cleared list, the DTC P0449 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0449 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
Is there a Current or Pending DTC P0449 set? | -- | Go to Step 3 | Go to Diagnostic Aids | |
3 |
Is the resistance within the specified range? | 25 - 30 ohms at 20°C (68°F) | Go to Step 4 | Go to Step 8 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 |
Does the test lamp illuminate only when the vent valve is commanded ON? | -- | Go to Step 8 | Go to Step 6 | |
6 |
Was a repair necessary? | -- | Go to Step 10 | Go to Step 9 |
7 |
Is the action complete? | -- | Go to Step 10 | -- |
8 | Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Is the action complete? | -- | Go to Step 10 | -- |
9 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 10 | -- |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | |
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
