Test requirements:

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2004 Audi A6, 2003 Audi S6, 2003 Audi A6, 2002 Audi S6, and 2002 Audi A6. However, it is still accessible from the selected car via links, so may be relevant.

Fuses for engine electronics OK
See appropriate Electrical Component Locator article.
Ground (GND) connections at engine and transmission OK
Battery voltage at least 12.7 V
Parking brake engaged.
Vehicles with automatic transmission: Selector lever in position "P" or "N".
Electrical consumers switched off (radiator fan must NOT run during test).
A/C switched off.