Where are the o2 sensors on 03 Audi A4 3.0 quattro?

On the 2003 Audi A4 3.0 Quattro, the oxygen sensors are located in two primary positions. The upstream (pre-catalytic converter) O2 sensors are situated in the exhaust manifold, while the downstream (post-catalytic converter) sensors are located after the catalytic converters in the exhaust system. Accessing them typically requires some disassembly of components in the engine bay or under the vehicle.