Audi Repair: P0421 Code - Check Engine Light - Misfire?, engine oil leak, vacuum leak

Question
Hi,  I had the malfunction display light up shortly after picking up a used Audi 2001 2.7 car from the dealership.  The car continued to run fine and the next day I stopped at Autozone to check the diagnostics.  The meter read the P0421 code which claimed it could be either

- A defective catalytic converter

- Engine Misfire

- Large Vacuum Leak

- Engine Oil Leak

I was wondering if there were other symptons I could look for to rule out some of these.  For instance, I checked the oil and it was fine with no change.  The car continues to function normally and I am wondering how I can know if its something major like the catalytic converter.

In addition, are engine misfires a serious issue to an engine and what costs can I expect for parts to put fix these issues.

Thank you.

Answer
hello
P0421 - on Audis is only one thing - bad cat. P0421 stands for bank 1 which is right side cat. You can reset fault and see if it comes back , if it does - you need cat.
I don't know where you live but in US CATS are under emission war. and are cover up to 8years or 80k. So if the fault is there just go to the dealer and they will do it for free. Most of the time your light will not come on, but there will be sporadic fault store in engine module.
good luck.             pltech