The wires in the valve circuit may be having problems.
Maybe the control solenoid is faulty.
The fuel cap may be incorrectly fitted or defective.
Possible solutions of the DTC code P0448 Generic
To troubleshoot faults caused by the P0448 OBDII error code, follow these suggestions:
Check the fuel cap. Make sure it is properly installed. Replace it if you find some problems.
Check for wires that rub against other components or have burn spots. If you detect defects, make the necessary repairs.
Inspect the vent valve for damage. If you find some damages, the valve must be replaced.
Check that there is continuity of the wires leading to the PCM.
Check the resistance of the breather with a DVOM. The result of this reading should be low resistance. If the value obtained is above the manufacturer's specifications, it indicates that a coil inside the valve is in bad condition, you should replace it.