Knock Sensor
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1993 Audi 90, 1993 Audi 100, 1992 Audi 100, 1991 Audi 90, and 1991 Audi 80. However, it is still accessible from the selected car via links, so may be relevant.
Knock sensor will produce a small voltage of about 50-70 millivolts if engine knocking is present. Check fuel quality, compression pressure, knock sensor and wiring circuits if knocking exists. No other tests are available from the manufacturer.