Audi Repair: Check line P0421 on and off, obd 2, autotap

Question
Hey,  I had messaged a few weeks ago.  I got the P0421 code and 2 days before I went to dealership (it has no warranty) the check engine light disappeared and naturally when they got the car they said it was fine.  The car ran with no problem and a friend of mine even had an obd-2 cable and Autotap software which we ran through the tests, found no codes and everything was fine with catalytic converter.

I took the car home and next day again, the code pops up.  It says the warmup efficency is bad on Autotap.  The light disappeared before and I m wondering if this is serious enough to warrant dealing with the dealer  (who is hour and half drive away) or if this is just a sensor bug.  Thanks.

Answer
hello
Like I wrote before P0421 stands for bad cat.If you reset fault and it comes back - you need cat. They run anywhere from $800 to $1400 plus labor (dealer price) I do not know where you live but in USA you will not pass inspection,
good luck            pltech