Code P0449 on your 2007 Chevrolet Trailblazer refers to the EVAP vent solenoid circuit, electrical fault. This fault could be caused by a failed solenoid, a wiring issue, or a faulty PCM. The solenoid should be located on the body cross member above the rear of the fuel tank. I did not find any service bulletins addressing this issue. I would recommend diagnosing the system before simply replacing the vent solenoid.