WARNING: This page is about a different car, the 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
Recommended special tools and equipment
VAG1526A multimeter
VAG1594A connector test kit
VAG1598/31 test box
Fig 1: Identifying Special Tools And Equipment For Checking Knock Sensors