Audi Repair: mil light on, catalytic converters, cat converter

Question
i have a6 quatrro 98 has 112000 miles in it..light on 100.000 iwent to dealer to check it when it off the say fond faults for warm up efficeiency for cat converter on banks 1 and2 but never get the code..it came back on for a day and off again..keep happening since then.so what's the problems?should i check it when it on?thanks...

Answer
The codes should remain in the computer, so they should still be able to retrieve the codes.  What kind of gas are you using?  It could be a poor grade of gas is affecting your catalytic converters.  Saving 10c at the pump is not worth risking $800 converters...  Let me know,  Jan