The gas gauge is stuck on one reading.
This is a common issue in GM vehicles. The instrument cluster in GM vehicles uses stepper motors to run the gauges. These motors fail often and make the gauges work erratically and give bad readings. The instrument cluster will need to be reconditioned for proper operation. The other part to the gas gauge is the sending unit. This is part of the fuel pump module. If the sending unit fails the reading sent to the cluster will be incorrect. Replacement of the fuel pump module is necessary for repair in this case. A mechanic such as one from YourMechanic can help you determine which of these two is at fault and suggest a repair.
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