The start-stop system helps to reduce fuel consumption and CO2 emissions by switching the engine off when the vehicle is at a standstill, e.g. at traffic lights. The start process is initiated as soon as the clutch is pressed (manual transmission) or when the foot brake is released (S tronic).

Increasing the generator voltage converts kinetic energy into usable electrical energy when the vehicle is coasting or braking. This (brake) energy recovery is then used to assist the generator during subsequent acceleration, saving up to 3 % fuel.

In this mode, the vehicle is adjusted particularly efficiently and the driver is actively supported with a driving style that can reduce fuel consumption. One example: the modified shift program with S tronic with a conscious movement of gearshift point in lower engine speed ranges. Here, the coasting mode of the S tronic is also activated, which means the vehicle clutch is automatically released when the driver takes the foot off the accelerator pedal, thus saving fuel. In efficiency mode, the electromechanical power steering system, cruise control and adaptive cruise control contribute to further reducing driving resistance. Equally, the air conditioning is adapted to requirements and switched to a working mode with improved energy consumption. The efficient driving style in the Audi drive select efficiency mode makes more mileage per tank filling possible, reducing CO2 emissions at the same time.

The dual-clutch transmission S tronic facilitates shorter gearshift times and gearshifting with no perceptible interruption in the power flow; can be operated via shift paddles behind the steering wheel, the selector lever or in automatic mode, includes hill hold assist.

Audi ultra, the pioneering lightweight technology from Audi, is also being employed in the Audi A3 Sedan.

The steel shell design of the Audi A3 Sedan combines low weight with high rigidity. Which type of material is used in which place on the vehicle is determined by the desired characteristics. The resulting material mix of hot- and cold-formed metal panels and profiles in the vehicle body create an ultra-modern lightweight structure. But not only ultra high-strength steels are employed, light aluminium is also used to reduce the weight of attachment parts such as the bonnet and front crash management system. The aluminium components on the front axle and the aluminium alloy wheels not only reduce the overall weight but also the unsprung masses, which in turn leads to a further increase in agility and driving comfort.

Modern TDI and TFSI engines in the Audi A3 Sedan also produce more power with a smaller engine size, making them lighter than the corresponding engines used in earlier model series.

Each lightweight component has an effect on other components, allowing their dimensions to be reduced as well. In the Audi A3 Sedan the lightweight body and lighter engines lead to secondary effects throughout the vehicle. The weight of many parts of the exhaust system, suspension and interior has been able to be reduced.