Hi,

Looked at the forum inside out and was wondering if I could get some help regarding the cat converters.

1) how many oxygen ports does a cat converter for a B6 (2003) a4 convertible 3.0 has?

2) where can I get a new/aftermarket replacement cat converter that will not through the CEL after instalation? Currently looking at either Eastern cats or Benchmark cats, but not sure how the CEL will react.

OR How and where can I change the ECU thresholds for the O2 sensors so the CEL doesn't come on after I install new aftermarket Cats?

Your help will be highly appreciated.

 

There are 4 O2 sensors on the 3.0 since it has true dual exhaust. When you replace these you need to make sure that you get the right ones for the front/pre-cat. They're a 5-wire wideband sensor. They are different from the 1.8t models. You do do not want to splice these. Just buy the whole sensor with the connector on the end. Do some research to make sure of the part# but it's a BOSCH part:

Fronts:
Audi part number = 06C 903 265 B
Bosch part number = 0 258 007 113/114

For the rears, I think those are standard 4 wire sensors. I spliced these with universal sensors and they're working fine for me.

As far as the CATS, OEM is the only way to feel most secure, but you may still get a CEL after replacing. I thought I was going to need to replace mine but after replacing all 4 O2 sensors and replacing broken vac lines, I'm getting good mileage with no CEL again. I'm at 184k miles, and I'm still thinking I may have to replace them one day. If so, I'm looking at the Eastern or PartsGeek CATS as replacements.

That's my 2 cents. Someone else can chime in and address the other questions. Hope you have VAG-COM software.

 

Thank you Shaundh.

Are both o2s located in the cat converter itself? I was only able to see 1 O2 for each cat, by the back engine. Driver's side was underneath the coolant resevoir, pass. side was by the air filter box underneath maf. Where would the other sensors be?

Also, were u able to see a difference on how the vapor was coming out of the muffler before u changed the O2s?

When I look at mine, I have unequal vapor that comes out of the two mufflers. The vapor coming out of the driv. side muffler, is less and also not as hot as the pass. side. No fuel smell though. This why I think that my driver's side cat conv is clogged expaining the P0431 code.

Let me know if u had the same issues. Thank you.

 

The sensors you can see are the rear O2 sensors mounted in the middle of the cat (dumb i know) the front ones are literally right where it bolts to the head. Look at pictures of the cat and you can see where the holes are, you actually have to remove the cats to get the sensors loose, at least thats what i do. Reach behind the heads and you can feel them.
www.partsgeek.com sells aftermarket cats, but they aren't CA legal, if you're not in Cali, then no biggie.

 

Thank you. I'm a NYC resident so the CA note is not applicable to me. Would you know how the CEL reacts to the aftermarket cats? I'm thinking Benchmark cats given that they load them up good - according to their description of course.
Also - do you know where around NYC, I can change the ECU thresholds of the O2s, so that the CEL is not triggered after I replace them? This will be resorted to in case the CEL keeps on turning on after I replace the cats.

 

The O2 sensors that you saw from the engine compartment are the rears/post-CAT O2 sensors. The fronts, you'll have to climb under the car and look above the axles on the exhaust to see those. The drivers side is somewhat accessable, but the passenger side is a real pain to get to. Don't know about the cabs but I had to take the axle and the guard around the axle off to get room to get an O2 socket around it with many different swivel extensions. I'll try to post my pics.

I did not notice anything with uneven exhaust, so you may be onto something. There is a test you can do in VAG COM to test the CATs for readiness. Check this post out at AudiWorld (the once great Audi forum) and read the instructions on how to do the readiness test. This may or may not give you the info you need:
http://forums.audiworld.com/showthread.php?p=22371381
I'm assuming you have access to VAG COM or the new version, VCDS from RossTech.

Also, are you experiencing any power loss?

 

Real pain to get to this one. Had to remove the axle.

http://forums.audiworld.com/picture....ctureid=229424

 

milltek makes some high flow cats. if you plan to mod later these might be the way to go. i don't know if they are the same flange to flange dimensions as the OEM.

 

Thank you Shaundh.

I have the ebay Vag-com hardware and I'm using the VCDS-lite shareware version. need to register/activate it I guess so I can access the cat testing. Usually after 50 miles local and highway, the readiness tests are all green/passed in vcds, and than after a few miles I get the CEL with the P0431.

As far as power - it depends. sometime it pulls very nicely sometimes is sluggish and the response to the throttle is not that fast. I revved the engine in neutral to max (gas pedal to the floor) and it didn't go beyond 7K RPMs. Not sure if it's supposed to go beyond that given that the RPMS end at 8K.
When you do the Cat readiness test with the break and throttle pedals depressed simultaneously, do you have the transmittion in P, N, or D?

 

You don't mention mileage, but they are warranted to 80k miles. I was one lucky sob since I found mine were bad at 79,800 and the dealer replaced them no charge.