Audi S4
Audi's quattro four-wheel-drive system was standard on the C4 S4/S6; a first-generation Torsen-based system which used the "T-1" automatically biasing centre differential (ATB) was used on vehicles equipped with manual transmissions, while a transfer box based system was used on vehicles equipped with an automatic transmission.
Audi S4
The S4 along with the other B8 models received a facelift in early 2012. This included a revised front-end with new headlights and grille, an updated interior, and upgraded MMI options. Mechanically, the facelift B8 (known colloquially as the B8.5) was upgraded with electromagnetic steering and a lighter crown gear center differential.