What does it mean when the fuel gauge doesn't move after filling up?

[VonArya]

The fuel gauge needle not moving is generally caused by a damaged fuel level float. If the needle doesn't move immediately after filling up, it's because the float is pushed to the top of the fuel tank by buoyancy, and the sensor-connected needle remains stationary. Only after some fuel is consumed and the float descends will the needle move with the sensor. Relevant explanations are as follows: 1. First, understand how the fuel gauge displays fuel level: it works via a float ball in the tank connected to a metal rod - similar to the mechanism in a toilet water tank. The end of the float-connected metal rod attaches to a variable resistor through a movable contact point. 2. As the float's position changes with the fuel level, the metal rod alters its position on the variable resistor. This variable resistor is connected to the vehicle's fuel gauge, and the needle movement is controlled by the amount of current passing through the variable resistor.