An all-new A4, debuted in late 2000, now riding on the all-new Volkswagen Group B6 platform. The car's new styling was a great success, inspired by the second-generation Audi A6.
Audi upgraded power in the 1.8 Turbo engines to 161 bhp and 187 bhp – the 187 bhp variant designated by a red 'T' on the boot lid, with both available with quattro, and in the 2.5 TDI intermediate version to 161 bhp. A 2.0 engine with Fuel Stratified Injection (FSI) was also available.
Audi also introduced a continuously variable transmission developed by LuK, named multitronic, which replaced the dated conventional automatic transmission on front-wheel drive models. The transmission won considerable praise from the automotive press, and is generally regarded as being the best of its type in the world, due to its light weight and promptness in response. This high strength chain driven CVT is made from highly durable metals and utilizes a very high grade, purpose-designed fully synthetic lubricant.
Borrowing from the Audi A6, the boot was redesigned to remove the extension of the top edge with a smoother fold line, and the rear light assemblies now formed part of the top line, these styling cues were eventually borrowed by other European as well as Asian manufacturers.
Source: Wikipedia, 2011