urban_legend

Warm-up catalyst bank faulty - I am guessing time to replace the cat.

Any suggestions on an aftermarket cat? 105 miles and only plan on keeping the car a couple more years.

Also, anything I should try first - before replacing the cat?

4Driver4

Year and model? O2 sensor checked? Not eligible for ECU reflash? Any other diagnostics done?

urban_legend

Details:

2000 A6 2.7T Quattro 6-Speed Manual
105,000
Error Code: P0421
Performance: Fine now, notice no difference.
However, for about a week it seemed to stall on start-up. (Like not getting enough gas.) Self-corrected.
Professional inspection: Not yet
ECU upgrade: Who is eligible - and how do I know if I am?
(I sent an email to the dealer but no word yet.)
Spark Plugs & O2 Sensors: Original (yea my bad - I never realized until last week that my plugs have never been changed. That is the problem with unscheduled maintenace you can miss the scheduled ones.) Anyway I am changing the plugs next week.

O sensors: Should I just change these as well?

emjayem

if you replace the cat, you may as well do the O2s as well. This code typically relates to a failing/failed cat.