Crashbot71

I've searched and read about replacing my catalytic on the forums but I haven't seen anyone mentioning about the O2 sensor location on top of the catalytic. I have a 2001 A8L and needs both cats replaced, the codes that I've been getting are similar to the ones that I've read about. I just replaced the front O2 sensors last month and I've been getting these codes since I replaced them:

16814-Catalyst System: Bank 2: Efficiency Below Threshold
P0430-35-10- -- Intermittent

16804-Catalyst System: Bank 1: Efficiency Below Threshold
P0420-35-10- -- Intermittent

I've reset it but comes back in a day or 2. I'm looking at a Magnaflow Catalytic as an after market, does anyone have a suggestion as to what aftermarket is best for me to use and what to do about the O2 sensor on top of the cats? Any help or information is helpful and thanks..

TerminA8r

Try one of these:
02 sensor spacer | eBay

Crashbot71

Are you suggesting to put one of these O2 sensor spacers on top or after the new catalytic?

TerminA8r

If the cats don't seem to be clogged (bogging down engine power), extenders would probably do the trick with the rear 02 sensors.

https://www.google.com/search?q=02+s...810&gws_rd=ssl

More info:
quattroworld.com Forums: non-fouler mod, or pony up big bucks for cats.. I did the non-fouler a few years back..

twentysevenlitres

You could also try replacing the rear O2 sensors (they lose sensitivity over time like the fronts do).
Cheaper than new Catalytic Converters.

Cats also clog up and their core can get coated with combustibles from the engine. Getting them nice and hot can burn all this coating off the core and make the catalyst do its job efficiently once more.
It requires a spirited drive - I find hill climbs the best, the longer the better, keep the revs up and the engine loaded.
When you get to the top, if you can smell the cats (sweet hot smell) you've done a good job!

tozoM8

After '00 they moved the secondary O2 sensors before the main cats to brag about the tumor size "efficient pre-cats" .