The fuel gauge only works when the ignition is switched on. Depending on the equipment fitted, the fuel gauge may be digital (bar display) or analog (dial*).
When the gauge reaches the reserve zone, the indicator lamp 
Link lights up in the instrument cluster display.
Link lights up in the instrument cluster display.The tank capacity of your Audi A1 is given in the Technical data section Link.
Caution!
Never run the tank completely dry. The irregular supply of fuel can cause misfiring, which would allow unburnt fuel to enter the exhaust system. This can lead to overheating and damage to the catalytic converter.