The most common reason for the fuel gauge in an Impala to stop at half full is a bad fuel sensor. The sensor is mounted inside of the fuel tank.
You can momentarily ground the power wire to the sending unit and the gauge should go to full.
Ground the power wire and have someone watch the gauge. If it goes to full then the gauge is working. Clean the ground connection and turn the key on and if it reads then it is okay. If not then you have a bad sending unit.
check your answer
It would be nice to have a few more details such as what you are working on. With limited details I will guess that your float/sending unit in the tank is malfunctioning. A second possibility is a bad fuel gauge if it is mechanical.
either the fuel gauge needs replacing or the fuel gauge sending unit in the fuel tank is stuck
A common problem with Honda cars is that the fuel gauge is stuck on full. This problem is solved by replacing the gauge cluster.
Your fuel sending unit is not giving the correct reading to your gauge
Check the fuel gauge sending unit, located in the fuel tank. The sending unit could be stuck in the full position.
There is no reset for the fuel gauge. The sending unit in the fuel tank has probably failed.
The 1997 Ford Explorer fuel gauge can be stuck on fault because the fuel float is malfunctioning in the fuel tank. The fuel gauge fuse might be blown.
Defective fuel sending unit.
If your fuel gauge is out of wack, go to the local parts store and orfer some fuel gauge wack. Pour it directly into the gauge until it is full of wack..........