# O2 Spacers



## IsaidWOT (Jun 4, 2014)

I had my car scanned for the check engine light and it's of course emissions. Which spacers do I need for the 3.0? The low profile ones or will the regular ones work? Also, is this really the downstream O2 right in front of the firewall?










Thanks guys! Been really helpful to me since it's my first Audi.


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## GLS-S4 (Jun 6, 2005)

Yes your pic is of Bx S2 which is post cat and is the downstream O2. The not-so-visible 3.0L upstream Bx S1 O2's are buried in the back of the head area. For example you could use a mirror on a stick between the head and firewall along with a lot of light to inspect where the cats bolt onto the back of the heads to see the upstream O2's.

What is your CEL related DTC(s) from your scan? Is it for failing cat codes such as DTC 16805 and / or 16815?

Of course for the 3.0 there are two schools of thought. One is the cat is truly faulty and needs to be replaced due to high mileage and failing emissions test or physical damage such as melted cats from continued driving with a critical fault like a failed coilpack and flashing CEL under acceleration. If so then cat replacement is the only real fix in order to restore normal vehicle operation. The other thought is possible Bx S2 O2 excessive tolerances along with the motronic engine computer programming of failed cat thresholds for the 3.0 in particular has been questioned over the years. I checked and as of two years ago Audi had not released updated firmware to loosen the tolerances of failed cat code DTC's on the 3.0, yet too many people who have replaced their DTC failing cats suspect there is nothing wrong with the cat. Ask any Audi mechanic that supports 3.0's if they have replaced what seems like a lot of cats on this platform. I'd be curious to hear from someone performing real world emissions testing on this platform for their observations.

Spacers may work but I've personally have not tried this on the 3.0. My 3.0 C5 A6 has DTC 16815 for one failed cat for the last ~25K KM's yet the pipe is not restricted and car runs perfectly. I don't like it but in lieu of cat replacement I was considering to try the $0.50 diode trick from the Audiworld link in the O2 sense wire and see what that does to the DTC. I too would appreciate any quality feedback and test results of various options so please chime in.


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## IsaidWOT (Jun 4, 2014)

This is the best answer I could have asked for. I'll have to look up the diode trick. We don't have emissions testing here in Michigan, US so I would be hard pressed to find somewhere to get it tested at. As for vehicle operation, it runs like a champ with no issues at all. I highly doubt that the cats are actually that bad as exhaust flow, power levels and mileage are all fine. If I figure anything out I'll update.

I purchased the diodes. I'll throw it on tonight and see if it gets rid of the codes.


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## IsaidWOT (Jun 4, 2014)

So the diode trick worked like a charm. Only difference I saw between my car and the 2.7T referenced in the article is the 3.0 only has the green connector, not a brown one.

Edit: so it didn't work. Wondering if there is a brown connector somewhere.


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## GLS-S4 (Jun 6, 2005)

Did CEL return and if so what specific DTC code(s) are being reported?


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