Just a WAG, but the gauge is actually driven by the PCM (or one of the other computers) IIRC. It is possible that there is a bad connection at the computer that is causing this.
I know my Dodge truck's fuel gauge is strange if I don't buy a full tank of fuel--it can take as much as five minutes to read the correct fuel level.
SELF TEST The instrument cluster self-diagnostic test will put the instrument cluster into its self-diagnostic mode. In this mode the instrument cluster can perform a diagnostic test that will confirm that the instrument cluster circuitry, the gauges, and the indicators are capable of operating as designed. During the test the instrument cluster circuitry will position each of the gauge needles at various calibration points, illuminate all of the segments in the Vacuum Fluorescent Display (VFD) unit, and turn all of the indicators ON and OFF again.
Successful completion of the self-diagnostic test will confirm that the instrument cluster is operational.
Begin the test with the ignition switch in the OFF position. Depress the odometer/trip odometer switch button. While still holding the odometer/trip odometer switch button depressed, turn the ignition switch to the ON position, but do not start the engine. Release the odometer/trip odometer switch button. The instrument cluster will simultaneously begin to illuminate all of the operational segments in the VFD unit, and perform a bulb check of each operational LED indicator. The VFD segments and LED indicators remain illuminated as each gauge needle is swept to several calibration points and back. If a VFD segment or an LED indicator fails to illuminate, or if a gauge needle fails to sweep through the calibration points and back during this test, the instrument cluster must be replaced.
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