The fuel level sending unit in the tank is probably at fault.
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.
Are you sure the fuel gauge is not the problem, maybe the tank is empty and the gauge is in error. If not get the fuel pump checked out, it is in the fuel tank and may have a broken pickup (in tank filter).
Bad sending unit. This is what reads the tank level and sends it to the gauge.
More often than not, a fuel gauge problem is usually a faulty fuel gauge sending unit in the fuel tank.
No there is not.
Generally the fuel gauge sending unit located in the fuel tank is at fault for incorrect fuel level readings.
Either the gauge or the sending unit is faulty.
More than likely the fuel gauge sending unit inside the fuel tank is shot.
It sounds as though your fuel gauge is wrong or more likely the fuel sending unit located in the fuel Tank is faulty. This Can be caused by contaminated fuel or just a malfunction of the unit
check for a damaged fuel tank
it is likely your fuel gauge is not working properly
Look for a bad grounding wire. If the fule gauge sending unti is properly gounded, it should send the signal to the fuel gauge, make sure the fuel gauge is grounded. You may have a bad fuel gauge.