Fresh styling and revised powertrains highlight a mid-2005 update for Audi's best-selling models. This line offers sedans, Avant wagons, and Cabriolet convertibles as A4 and high-performance S4 models. A4 sedans and wagons at midyear traded a 170-hp turbo 4-cyl engine for a 200-hp turbo 4-cyl to become 2.0 T models. V6 versions exchanged a 220-hp V6 for a 255-hp V6 to become 3.2 models. S4 versions retain a 340-hp V8. A4 and S4 sedans and wagons get a lower-body restyle marked by a large vertical grille. Interiors are revised, brakes are larger, and new options include steering-linked xenon headlamps and heated rear seats. Similar changes are due for 2006 for the A4 and S4 convertibles. For now, A4 Cabrios retain the 170- and 220-hp engines.

Audi's quattro all-wheel drive is standard on wagons, 3.2 sedans, and S4s. It's available in place of front-wheel drive on 2.0 T sedans and V6 A4 convertibles. Front-drive models offer a 6-speed manual transmission or a continuously variable automatic (CVT), depending on model. The CVT provides variable drive ratios, plus six preset "gears" selected by floorshift or steering-wheel buttons. All other models offer the 6-speed manual or a conventional 5-speed or 6-speed automatic. S4s have unique trim, sport suspension, and 18-inch wheels. Other models use 16- or 17-inch wheels and offer Sport Package options that include a firmer, lower-riding suspension. Every A4 and S4 comes with antilock 4-wheel disc brakes and antiskid system. Sedans and wagons add head-protecting curtain side airbags and front torso side airbags; rear torso side airbags are available. Convertibles have front side airbags covering head and torso, plus rear support bars that pop up automatically for occupant protection if sensors detect an imminent rollover. Cabrios also have a power fabric top with heated glass rear window. The available navigation system includes Audi's MMI operating system that uses one knob on the center console to take the place of conventional dashboard controls for many of the car's accessories.