P0449 refers to the EVAP Vent Solenoid Control Circuit.
From the manual:
Battery voltage is supplied to the EVAP canister solenoid valve. The ECM grounds the EVAP canister vent
solenoid valve control circuit through an internal switch called a driver. The ECM monitors the status of the
driver. A scan tool will display the commanded state of the EVAP canister vent solenoid valve as ON or OFF.
CIRCUIT/SYSTEM VERIFICATION
1. Ignition ON, engine OFF, command the EVAP vent solenoid ON and OFF with a scan tool.
2. Listen for a click when the valve operates. Verify that both the ON, and the OFF states are commanded.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within
the conditions that you observed from the Freeze Frame/Failure Records data.
CIRCUIT/SYSTEM TESTING
1. Ignition OFF, disconnect the harness connector at the EVAP canister purge or vent solenoid valve.
2. Ignition ON, verify that a test lamp illuminates between the voltage supply circuit terminal A and ground.
If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an
open/high resistance. If the circuit tests normal and the voltage supply circuit fuse is open, test or
replace the EVAP canister purge solenoid.
3. Connect a test lamp between the voltage supply circuit terminal A and the control circuit terminal B.
4. Command the EVAP canister purge solenoid valve to 50 percent with a scan tool, or the EVAP canister
vent solenoid valve ON and OFF. The test lamp should respond to the command.
If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests
normal, replace the ECM.
If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the ECM.
5. If all circuits test normal, replace the appropriate solenoid valve.
