Today when I went out in the car I spotted that the fuel gauge, instead of reading just over a quarter full was reading just over half full. When I came out of the shops and turned the ignition back on it reverted to reading the lower value.

My question is,: Does it require the full gauge to be reading correctly for the low fuel warning display to to come on at the correct level? An erratic fuel gauge is not a problem as long as the warning light operates as it should.

I always reset the Multi Function Display memory 2 when I refuel so it gives me an approximation of how many miles I have left in the tank so I am not completely in the dark.

I had a similar situation once, a VCDS scan revealed something to do with a fuel level sender sensor or something like that. I think the whole thing is a unit, pump, sender etc. I might be wrong. I cleared the codes and never came back again, but I do notice that I do about 350mi all the way to the half marking, then about 50 from there to reserve warning. 

 

To answer your question, possibly yes. the warning might be triggered by the indicator reaching the mark. All to do with the sender.

My fuel gauge is considerably more linear than that. At just above a quarter I have done 300 miles and the MFD says I have about 100 miles left.

that's 100 miles with reserve. Sounds about right?