Hello. I have S3 8l AMK engine full stock except S200 filter. When I bought the car the rearo O2 wasn't working. I replaced it with new Bosch. And then I got error in VCDS: 16804 Catalyst System; Bank 1: Efficiency Below Threshold Then I de-cat and put 2 straight pipes cause of the twin cat's. Ever since I put the new O2 sensor and got this error the car goes into limp mode. Clearing the DTC is the only fix. Restarting the engine doesn't work. Sorry for my English.