In this video we go through the steps of replacing the bank 2 (post-catalytic converter / downstream / rear) Oxygen Sensor on a 2012 Audi A4 (applies to entire B8 generation, 2008-2016 models).
If you are getting a “P0430 – Catalyst System Efficiency Below Threshold (Bank 2)” warning from your OBD scan, this could solve your issue and get rid of the engine light.
This is the more difficult sensor to replace however the same general steps can be used to replace the bank 1 / upstream / pre-catalytic / front converter sensor.
The O2 sensor measures the amount of unburned fuel in the exhaust pipe to adjust fuel mapping for less emissions and better fuel economy. When malfunctioning, your MPG and performance can suffer. Replaced fairly easily, you can restore your performance and mileage quickly. Be sure to add anti-seize on the threads to prevent it from becoming a permanent part of the exhaust.