Fuel gauge on my 2002 Buick Regal, drastically fluctuates, sometimes even causes the EMPTY signal to sound…and the mileage range indicator DROPS from 21.6 to 16.3. HELP!!
I can’t be 100% sure, but usually on GM cars from this era, what happens is that the fuel level sensor goes bad.
A “float” which literally floats on top of the gasoline inside the gas tank is mounted on the end of a short “arm”. The arm attaches to a plastic piece with an electrical device that alters an electrical signal, as the level of gas goes up or down, and that gets transmitted (sent) by wires to the gauge and miles/per/gallon indicator.
Little “fingers” (fine wires) in the sensor (sender) device move across (wipe) a small section of the device and that’s what alters the electrical message. Those little wire fingers eventually wear out or dissolve and contact becomes very intermittent and unreliable as shown on the dashboard.
Usually on cars the solution is to remove the entire gas tank from the car and replace the entire fuel pump module that includes a new level sensor. Parts and labor would be in the hundreds of dollars.
However, I believe that you are fortunate! Under the rear trunk mat of your car, on the floor of the trunk, between the spare wheel well and the rear seat, you should be able to locate a small oval plate secured with half dozen or so small screws or nuts. See if you can find it. That is a convenient access panel for the fuel pump module/fuel level sensor (sender).
With the plate taken off, a mechanic can remove the pump’s lock ring and withdraw the pump/sender assembly. The gas tank does not have to be removed!
Now, instead of buying the whole fuel pump module/fuel level sensor (relatively expensive part), you should be able to buy and have replaced, just the level sensor. It’s less than $40 for the part.
Do you have a regular mechanic you use for maintenance and repairs? I’d run this by her/him and see if they’d be willing to diagnose the problem, and if they confirm the sensor is bad, replace the sensor as I’ve outlined. Perhaps they can give you a complete estimate which includes labor.