Fuel gauge stuck on full

You float is stuck. These older cars just have float arm with a sensor that sends a voltage to the fuel gauge. The higher the fuel the higher the arm which lowers the resistance in the circuit. This sends more voltage to the gauge which puts the needle higher on the gauge. The lower the arm, the more resistance which lowers the needle on the gauge.

More than likely you just need to replace the sender in the tank if the reading is the only thing wrong. If the car starts and runs fine then it is just stuck and needs replaced.

If that is the case, we will want to physically check the float to see if it is in fact stuck. If it is then I would have it replaced because it will just keep doing it. There is a chance that if you "unstick" it that it won't do it again, but I wouldn't want to take that chance and have to drop the tank again.

If it is new then it should still have a warranty and they will take care of it.

Unfortunately there is no other way to fix it for sure.