I put on a Mr Exhaust catalyst on my A6 4.2. The code below efficiency threshold comes on since after just a hundred miles. Has anyone gotten an aftermarket cat to work? people are talking about reflashing ECU. How? spacing out o2 sensor?

 

I think using spark plug non-foulers may be the solution. However, did you try clearing the code see if it comes back?

About three monts ago I replaced the whole exhaust (including the cat) in my Elantra and I got a CEL within 50 miles, just as the vast majority of other people who replaced the cats with aftermarket ones reported. I cleared it and never came back.
I would say it may have something to do with a "break-in" condition, but I don't want to sound stupid.

 

Maybe it has something to do with touching the sensors. The grease on them might cause them to arc more until they have heated up. You know they had to spray the crap out of them when removing them.

 

I have reset the code many times. it comes back in about 100 miles. the car is otherwise free of issues and codes. I like the grease theory (but shouldn't it burn off from the heat?). I'll try to take out and clean the front sensor. I guess for the rear sensor, the dirtier the better?
If that doesn't work I will try the spark plug non fouler at the rear.
Thanks for the advice!

 

I replaced with an after market cat, no problem, but he after market O2 sensors had to be replaced with audi ones for the codes to stay away.

 

Didnt auditech say something about the ECU needing to be reflash with a higher set point for this? Its in a TSB or something.. Its in the forums here somewhere...

 

Just purchased an 03 A6, failed smog (P0421 & P0431) at my local shop and brought it back to the where I bought it (used car dealership). They replaced the 2 cats and the code is gone, according to my shop the new CATs are still showing a fail on the machine. They suggested to try to drive another 30+ miles to see if they "Set", this is the same thing I was told by the dealership.

Any thoughts?????? I have already driven over 60 miles on a single trip.

 

I have 2 aftermarket cats for maybe 1 or 3 k miles now with no problems. IIRC I used magnaflow or something like that. I never got any codes.

 

Your readiness code needs to set. Do a forum search.

 

O2 spacers (mini cat) eliminate cel: www.bigdaddiesgarage.com

A6 needs 2