Gas guage is crazy

I have a 2006 GMC Envoy Denali XL and when I fill my tank up the gas guage goes crazy. It flips from full to empty to full and the engine light comes on at times. Once I reach a half tank everything is normal. Does anyone know of a product I could try before taking this car back into the dealership for a big $$ repair.

Sometimes a bottle of Techron in the tank, if the problem is sulfer content.

If this is an electrical problem it is likely a faulty ground in the circut for the gas guage, no clue about the “engine light”.

It is out of warranty I assume? How many miles?

It’s far more likely to be the variable resistor of the fuel sender in the fuel tank. That’s why a fuel cleaner might restore proper operation.
A bad ground wouldn’t care how much gas was in the tank.

It is out of warranty car has 80k miles. The engine light doesn’t come on all that often only when I top the tank off. What I do now is check how many gallons I use and then reset that everytime I fill up. The needle just goes from full to empty to full to empty and then once I’ve been able to burn some fuel it all goes back to normal. I’ll try the Techron and see if that helps. Thanks

vacuum in the gas tank maybe ? I read a post on another discussion that said to not tighten your gas cap all the way just enough to sty on and allow air in and see if it goes away

that’s interesting and new i just may give that a try. thanks