Gas gauge only works from 1/2 tank to empty do you know why

Either the fuel tank sender in the tank is bad and needs replacement, or the fuel gauge is faulty. I would bet the one in the tank is probably bad, because that's usually the case. Find the connection at the fuel tank, disconnect it and use a VOM to get a resistance reading while the tank is empty and reading 1/2. It should match the specs.

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It could be the sending unit in the tank or the gauge on the dash. A mechanic would test the signal coming from the sending unit to verify.

You will need to replace the fuel level sensor, this involves the removal of the fuel tank to access the sending unit.

It sounds like the fuel sender is bad in the fuel tank.

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.

Fuel sensor is not working well. Just changed mine today for the same problem.

Sounds like the sending unit is bad in the tank.

Fuel level sending units are known to go bad on these.

sounds like a faulty float on the fuel pump not sending the correct signal to the guage. if helpful please rate

Is......the problem--"the gas gage reads empty when there is fuel in the tank. OR, The gage moves when the key to turned off ?

If it's the first,
You will need to test the gage and through process of elimination, determin if the Sending unit inside the fuel tank has gone Bad.

If its the second ? - Electrical gauges will move when powered down. Normal

Testing the gauge may not be easy - just depends on your ability.
It is a simple 2-wire gauge circuit, when disconnect (usually need the fuel tank) the gage reads in one direction (either full or empty)
then when shorted-the gage reads in oppisite direction.

Of course you must select the correct wires or you may short out the wrong circuits!! Most GM vehicles use a purple wire & black wire.

A quick method I have used to check the in-take part of the gauge is this.
1st. know there is gas - 1/2 tank works best.
2nd driver's door open, key in run position, engine not running.
3rd gently lift up on the door then let if come back down, gently.
just enough to cause the gas to slosh around.
4th - keep an eye on the gas gage, a bad sending unit in the take will show up as a "twitchy" needle.

Of course, if the gage never leaves empty - sloshing won't work.
I have a known good sending unit I can plug into the vehicle and simulate different levels of fuel - if the gas gage works, I know the problem is in the tank.

Let us know.

Dave