The OBD-II trouble code P0463 in a 2003 Buick LeSabre indicates an issue with the fuel level sensor circuit. This code is set when the engine control module (ECM) detects a voltage signal from the fuel level sensor that is out of the expected range. This can be caused by a faulty fuel level sensor, wiring issues, or a problem with the ECM itself.

To diagnose and repair this issue, you can start by checking the wiring and connectors related to the fuel level sensor for any signs of damage or corrosion. Ensure that the sensor is securely connected and there are no loose connections. If the wiring appears to be in good condition, it may be necessary to replace the fuel level sensor itself.

It is recommended to clear the trouble code after any potential repairs have been made and monitor the vehicle to see if the issue persists. If the code continues to reappear, further diagnostic testing may be required to pinpoint the exact cause of the problem.