The fuel gauge is a small part with a big job. It tells you how far you can go before the car needs fuel, and when it starts lying, the first thing to break is your planning. Gauge trouble is easy to ignore because the car still runs. That is exactly why it is worth catching early.
What the gauge does when it starts to go
Gauge trouble rarely arrives all at once. Watch for the needle sitting high right after a fill-up and then sinking faster than your driving explains. Watch for it reading empty while the car keeps running for a long stretch. Watch for it jumping on a hill, a sharp turn, or a rough road. Watch for the low-fuel warning coming on at a different point each time, sometimes too early to be useful and sometimes too late to help.
Check the gauge against your own math
Keep a simple note for a few weeks. Write down the odometer reading at each fill-up, the gallons you put in, and where the gauge sat when you stopped. Divide miles by gallons to get your own average. If the gauge drops much faster than that average says it should, or if it reads empty long after the math says fuel remains, the gauge is telling you something is off. Your note is also the record a shop will ask for, and it is far more useful than a memory that the car felt odd.
Separate a gauge problem from a fuel problem
A gauge that misreads is not the same as fuel that leaks. If you smell fuel near the car, see wetness under it, or notice the level dropping while the car is parked, stop treating this as a reading issue. Park somewhere safe, keep away from open flame and sparks, and have a shop inspect the fuel system before you drive again. That is a safety call, and no contract question should delay it.
What a shop will need from you
Ask the shop to test the fuel level sending unit and its wiring, and to write down what they found and what they replaced. Ask for the estimate in writing before any work begins. If the car is under a service contract, ask the shop to note the diagnosis on the repair order, because a claim usually depends on paperwork showing what failed and why. Keep copies of everything. A contract will not help much if the paper trail is thin.
What to check in the contract
Gauges, warning indicators, and sending units are parts that some contracts list as covered, some leave out, and some cover only when they fail along with a covered component. Do not assume. Find the covered parts list, then search it for the words fuel, gauge, sending unit, and instrument cluster. Read the exclusions next to the list, since an exclusion can override what the list seems to promise. Ask the seller to point to the exact clause in writing. If the answer is vague, treat the gap as yours to carry.
Where to look before you sign
Ask how the contract treats a diagnosis that finds a covered part and an uncovered part at the same time. Ask whether the shop may begin diagnosis before the claim is approved, and who pays if the diagnosis finds nothing wrong. Those answers decide whether a gauge repair is a small bill or a surprise. Read the sample contract if the provider publishes one. This site's list of providers that post a sample contract shows which companies let you read the terms before you buy. The published figures for each company are in this site's tables, and this guide does not repeat them.