2005(B6) Audi S4 - Gas gauge

Question

The gas gauge in my audi just kinda stopped working.

By kinda, I mean that, before when I would fill up gas all the way, the gauge would sit really close to the F mark.

Now, whenever I fill up and the gas pump automatically clicks and shuts off, whenever I start the car, the gauge only goes up the 3/4, sometimes less.

I tried filling up again, but it just starts overflowing.

Whenever the gas light comes on, I pump gas and it only costs me about $20, when I know it should cost more.

Let's assume it's the gas gauge sensor, since I'm not sure what else it could be.

QUESTION

If the gauge is malfunctioning or not working properly, does that affect the gas pump from "knowing" when to stop pumping gas or how does that work??

And if my gas light is coming on, could it be possible that if the sensor is malfunctioning, that I actually do have more gas than indicated, just that the sensor is broken??

Answer 1

The pump cutoff is completely independent of your car, it's based on air pressure and has nothing to do with your gauge.

What you describe does sound like a bad fuel level sensor rather than the gauge, usually gauges will stick when they break or just go dead. Your gauge is registering some changes, although it doesn't register full and it reports low fuel when it's not close to empty. It's one of those things that generally isn't worth trying to repair, I'd replace it. In the meantime I would use your trip odometer as an indicator of how much fuel you have left. Make sure to reset it every time you fill up.