IF your car has a 55L tank, as does my Plus 8 then the low level light comes on constantly when there is 5L left, so 50L used. it will come on and go off, depending on gradient, acceleration and braking, with about 45L in the tank.
I confirmed the 5L left by adding close to 50L to the tank when the light had been steadilyon for about half a mile.
The Plus 8 has BMW electrics including fuel tank sender, pump, etc. It has a fuel gauge that is accurate, displaying both graphically and as a percentage, to the point that I trust the information as I do in any modern car.
