Well my CAT is bad have the PO420 on for a bit now, I have an 03 A4 1.8T AWD I want a stock replacement how many O2s are there on the stock cause I seen some options with one wanna make sure I order the right part

 

There are 2 o/2 sensors. One before & one after.
Use dealer only cat or you will be doing it again next year. Most aftermarket cats have about 1/2 the internal material of a OE cat.

 

Most of the time that code signifies a bad cat. No the sensor. But u can replace the sensor and see how that goes. If it dont work u can try to use a o2 spacer on the sensor to get the right readings or go dp or hfc tp .

 

The indie shop that does all my work told me the O2 sensors are good for about 100k miles. I just replaced my cats (P0420 and P0430) with a Billy Boat downpipe kit and replaced all four O2 sensors with oem Bosch. The bad news - I still get the CELs after driving ~100 miles. Researching why.

 

Billy Boat Down pipes? Bubba billy is making catalytic converters. Converters should be dealer only. Most aftermarket cats do not have as much material internally as oem cats. That's why they are cheaper because they are cheaper , don't work as well or last as long!

Also might want to check for software update. Audi has a software update to correct p0420 & 430 codes on some vehicles.

 

Have you tried to using the 02 spacer? it might rid your cell.
Test Pipe p0420 fix?
http://forums.evolutionm.net/evo-how...cel-light.html

 

I'm guessing software update is.dealer?

 

I might do that spacer and return the cat what do you guys think?

 

Might be worth a try.

 

i would run the spacer first before u return the cat.