audi tt 2003 smogtest
 

why is my audi tt 2003 cant pass smogtest according to the technician due to catalyst

Probably need a new cat.

Many advocate replacement. I was told same years ago and found other repairs cleared up the DTC for the cats. Depends on how much time and work you want to put into it. We have 3 Audis of this vintage all with over 200,000 miles all on original cats. None have engine issues. But I do understand if you do not solve performance related codes quickly the cats can definitely be ruined while you procrastinate.