I have a 2001 A4 2.8. I was searching like crazy and i found some info for the 3.0 engine, but not the 2.8. I'm trying to replace my bank 1 post-cat O2 sensor and I cannot find it for the life of me. I looked from the bottom of the car, there's the 2 cats, and the driver's side cat has an O2 sensor right before it, but nothing at all on the passenger (bank 1) side. Can someone tell me where it is? thanks

 

The post cat O2 sensors are the ones you can see under the car, the before cat O2 sensors you can only see from the engine bay.

 

2 before on the downpipe, 2 right after there all easy to see