The fault code P0449 OBD2 is a generic code and means that the PCM (Powertrain Control Module) has detected a fault in the circuit that controls the ventilation for the vapors in the steam emission system.
When the fuel begins to settle in the tank, the fuel vapor is expelled. As the vehicle is running, the vent opens allowing the vapors to circulate either to the intake manifold, the active carbon filter, or to the atmosphere, depending on the model of your vehicle.
This ventilation valve, although it is simple, it is part of the complex EVAP system (Evaporative Emission Control System).