Most likely either a bad float in the fuel tank or defective gauge
It takes a special gauge to install the crank sensor. It can be rented from some parts stores.
Depends on what year Cutlass Supreme you're referring to...
cutlass supreme,is under glove box,lift up the front and pull up.
i have 1991cutlass supreme v6 my digtial gas gage stuck
If your battery was dead and you jumped it to get it started and the gauge shows your not charging you need to replace the alternator.
If the gauge is reading hot and the car is running normal temperatures, the water temperature sensor needs replaced.
I have a 90 cutlass supreme. Mine has been going goofy for some time now. If it blacks out, flashes off and on, or shows different readings on fuel gauge, odometer or speedometer then you have problem. I took it out and looked for loose plug wires(1 plug) or cicuits. Found none. Needs replaced. Can sometimes be found on Ebay for cheap price. If so make sure it right one!!!
The color of the wire going to the fuel tank sending unit from the tank level instrument on the dash is taupe (or light tan). 1970 Olds Cutlass SX
Stick a peace of wire threw the hole of the mileage reset button and push it over.
The fuel pump is located in the gas tank. 1996 & up you can access by removing the back seat. Your model (same as mine unfortunately) needs to be jacked up so you can drop the tank & remove it from the top. Since we did mine the gas gauge is off by 1/4 tank (found that out the hard way) so be careful with the float.
The speedometer and gas gauge going out tat the same time indicate an electrical problem. The instrument cluster may have to be removed and the circuit board checked for loose connections or cold solder joints.
In front of the radiator