the gas gauge lights half the unit then gauge will jump full/empty on 2000 Buick LeSabre

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The gas gauge is going crazy - it will illuminate only half of the unit, and can jump to full after driving for many miles, and then back? What is going on and what will it cost to fix?? Thanks
(1) Answer
Chances are the fuel level sensor located inside the fuel tank is failing. If that is the case there should be a fault code stored in the powertrain control module (PCM). Your first step should be to have the fault code(s) read from the PCM and properly diagnosed. Let's not begin replacing parts until we are sure what the problem is.