Fuel gauge inaccurate & warning light always on.

Without testing we'd only be guessing . Hooking up a factory or a professional type scanner , an checking engine sensor data parameters , checking fuel pressure an flow , basic electrical system testing - battery condition , charging system output testing etc.... GM did have instrument cluster problems , late 90's - mid 2000's . Stepper motor's inside the cluster that drive the gauge needles , an silver migration . Can cause all kind of electrical issues , battery draining over night , starting problems ,warning lights coming on etc....
How to repair GM Instrument Cluster Speedometer Gauge Stepper

Your best bet , take your vehicle to a qualified repair shop.

It is in the instrument cluster, which has to be removed to replace the gauge. It cannot be repaired. Did you first check the 10 amp METER fuse in the fuse panel?

Now let me say, that when the gauge quits, it is more often a fault in the sending unit in the gas tank, and not the gauge. Here is how to find out if your gauge is good: Find the fuel tank electrical connector, and pull it apart. You will need a small jumper wire. Find the blue wire in the body side of the connector (not the fuel tank side). Put the jumper wire into the blue wire terminal, turn the ignition key to on not start, and ground the jumper wire to a metal frame piece. Someone needs to watch the fuel gauge needle while the wire is grounded. If the gauge in the dash is good, the needle will move. It will probably go to either full or empty, but if the needle moves, the gauge is good and the fault is in the sending unit in the tank. Don't give up testing until you are sure the jumper wire is being grounded good to the frame. Just touch the wire to frame and watch the needle movement, once sure, stop so you don't blow the fuse. If the needle doesn't move, first check the 10 amp meter fuse. If fuse is good, it must be the gauge.

To get a free diagnosis from dealer,take for oil change only,don't say a word about your problem,they will find it and also do a full scan on it and tell you what is wrong and how much to fix,sense you brought in for oil change,you have the option of letting them repair or telling them your not able at the moment and repair yourself,I get my vehicle's oil change at Dealer always,free scan.Me smarter than them.

Look for a problem with the fuel level sensor wire or a bad fuel level sensor. It could also be a failure right in the fuel gauge. Your model probably uses a direct metering (analog) gauge*. These have wire-wound resistors inside that sometimes burn out or break. If the low fuel warning light comes on when it's supposed to, then the problem is the gauge itself.

*Some of the newer GM models starting in 2001 have replaced analog gauges with digital circuits using stepper motors to drive the gauge needles, and they've had reliability issues with the stepper motors.

i had the same problem, it turned out that the float in my gas tank was so old that my gas gauge on the dash was inaccurate. so it only happened wen it was less than a quarter tank of gas on the gauge but really i was out of gas and the gauge was wrong

ZAS

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

You have a fuel gauge sending unit problem, the gauge is not the problem, the sending unit is in the gas tank, u must remove the gas tank to replace it.

Sure there is!

DO THIS FIRST!!!
When you turn the key on, and the gauges and warning lights come to life, does the needle on the fuel gauge move a tiny bit? It should. If it does move a hair, this is a good sign your gauge is still good. If not, keep reading.

The gauges themselves are usually not at fault, but they can fail, of course. Usually, it's the sender or float that's the culprit. The assembly resides in the fuel tank in the module or unit that houses your fuel pump. Many customers (when faced with the cost of this tank job) will opt for waiting until the fuel pump goes bad, and replacing pump and sending unit together. However, there are obvious drawbacks to this!

ONE test you could do if you are good at driveway car work is this: Crawl under vehicle and find the bundle of wires (not tubes or lines) that goes up to the top of the fuel tank. Sometimes you can reach it through the rear wheel well. Follow this small group of wires up to wherever it plugs in to the pigtail coming out of the tank. THis could be on top of tank, or just outside the perimeter of the tank. Unplug this connection. Using a common 12 volt test lamp probe, ground the test lamp, turn the key to the "ON" position so dash lights up, and touch tester to each wire tip on the end not connected to the tank (engine side of wire harness.) Have someone watch the fuel gauge as you touch the leads one by one. The gauge should move when one of these is grounded thru the lite. Total deflection of the needle means your sender is at fault, not the gauge. BUt it's usually the sender, anyway. THey're cheap enough, but the labor on a tank job can vary from place to place.

Good luck, TT

the fuel gauge and fuel pump is one assembly in the fuel tank. You will need to drop the fuel tank. May be a loose connection or faulty sending unit