I have been browsing the threads, but still am looking for an answer. I have a 2000 A6 2.7T Quatro with 102K miles, and I am looking for the oxygen sensor past the CATs. I can clearly see the two in front of the CATs, but I am unable to find the post CAT sensor.

I have heard that this car only has the three, can anyone direct me to where the third post CAT sensor is located? I have followed the twin exhaust back to the mufflers, and I am confused. Any help would be appreciated.

I have error codes of
P1122 O2 Sensor Heater Circ.,Bank2-Sensor2 Open and
P1140 Bank2-Sensor2 Internal Resistance too High ( assuming its bad, but I wanted to check the wiring and clean it first.

I am also getting

P1136 Long Term Fuel Trim Add.Fuel,Bank1 System too Lean

P1138 Long Term Fuel Trim Add.Fuel,Bank2 System too Lean
Assuming these are the two fronts, once again, I wanted to clean instead of change at first.

I see some talking about the cheaper universal sensors, but the wires need to be spliced. I am capable of doing that, I just wanted your thoughts on if its worth the cost difference to buy the BOSCH ones and fight the cable ties to replace the sensor and cable?