Long time browser of the forum but first time posting, hope you can provide some advice
Put the car through an MOT yesterday (2001 S3 Totally standard recently serviced etc) and it passed on everything except the emissions, the mechanic who i took it too (Deutsch tech local audi specialist) ran some injector cleaner through the car and gave it a good run and warm up but failed again on the second attempt.
Im getting some mixed opinions on how to get the emission levels down, the mechanic who i took it too doesnt think the lambda probe is faulty as he can see it 'switching' and thinks the cat is by its best and needs replaced. A few other people i have spoke with reckon that the cat shouldnt fail and it will be a probe, i have ran vagcom with no errors returned.
Does anyone have any advice before i spend any money on what this could be, are the cats known to fail on the s3? at the moment im thinking of going down the lambda sensor as it would be the cheapest.