My gas gauge was on full and dropped to empty. hen

Grounding is very important with sensors, especially with fuel systems. Your sensors could be defective as believe it or not, they do wear out or your float is sticking

Bad sender unit in gas tank

weird...first thing to do is get a scanner hooked up to see what caused the check engine light-free, at pretty much any retail auto parts operation-i wouldn't get overly concerned with the gas gauge right now, teh code that tripped the check engine light might explain that problem.

fuel level sensor is part of the fule pump assembly. code is telling you sensor is malfuctioning. do gauges work? if yes i would leave problem alone till you need a fuel pump

very common. The sender in the gas tank is the problem.
It will need to be replaced some day
Both my gas tanks do the same thing in my F250. 1 tank stays full all the time and the other drops from full to about a half tank when I get to half a tank and then works so so till empty.

sounds like a bad ground in the wiring.

the problem is caused by a defective gas gauge sending unit, this part is located inside the gas tank, you must remove the gas tank to replace it.

did you replaced just the float , because if the resistor that messures the level is not good you didn't do any thing you have to change the level sensor next to the pump..,Im sure that;s all the problem, you should also check the wiring next to the pumpand any connector down there

the fuel gauge sending unit in the gas tank is a mechanical part, but you may have an electrical problem. the needle is moved by an electrical signal. you can check the wires coming out of the back of the gauge, one will run to a chassis ground. make sure that wire has a good connection to ground, first because it won't work right without it and second because it's lots easier than the next thing you will have to do if that doesn't make an improvement. if you see no difference after checking the ground then you need to drop the tank and replace the fuel level sending unit. you will have to remove the fuel pump to get to it so you might want to replace it while you have it out, that's your call. your vehicle is new enough that the decision would be more based on miles than age. hope that helps

Sounds like the gas tank sending unit went bad.