Problem with Audi A3 Fuel Light

[boson]

My fuel light keeps coming on even though the gauge says I have half a tank of petrol. I'm sure the problem isn't with the gauge as it gradually goes down the more I use it.

Any ideas?

I have the 2000 1.8 sport model, petrol

 

[boson]

i've managed to fill up the tank meaning the problem is with the gauge, not the warning light

can anyone help?