# Fix check engine light from non OEM Catalytic Converter Audi A6 1999 2.8



## Daddioman (Apr 19, 2007)

The dealer wants over $2000 to replace my (2) catalytic converters: Audi a6 Avant Quattro 2.8L 1999, 88,000 miles. They sell the converters for like $800 a piece. The Internet tells me there are all kinds of replacements out there some for less than $100 each. I have two concerns: 1. How difficult are these to replace. It looks like the whole exhaust is one piece. 2. Do any of the cheaper replacements out there have the electronics / plug in necessary to keep my check engine lite off? Or is there another way to fix that ? I am a novice repair guy, but I can work my acetylene torch. Thanks! Appreciate your help. Also have a topic started on will spark plugs fix my chugging, and a question on changing out my control arm.


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## mobilize325 (Aug 27, 2007)

*Re: Fix check engine light from non OEM Catalytic Converter Audi A6 1999 2.8 (Daddioman)*

i am having the same issue with my '00 passat. My engine light is on due to the cat and the dealership wanted well over 2k for the fix. I considered getting a whole new custom exhaust done but then i face the engine light problem and it not passing the damn NY state emissions (which is wont as is anyway). Is there possibly anything else i can do to fix this problem.. the car runs great regardless but i need that light gone. Any advise would be great....and i feel your pain.


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## Funkatollah Insaney (Aug 17, 2004)

*Re: Fix check engine light from non OEM Catalytic Converter Audi A6 1999 2.8 (mobilize325)*

The DTC light associated with bad cats is from a double check the ECU does to make sure the cats are working. It looks for a delta, in a range, between the 2 O2 sensors. This delta has fallen out of range. There was a recall/ campaign a while ago for bad catalytic converters that were actually a faulty code in the ECU.
If you were to come up with the cats on your own and then have an exhuast place install them, it would be significantly less than the dealer. Any reputable exhaust place will be able to furnish locations for the O2 sensors on each runner as well. 
Check to see if your car falls under the faulty ECU coding first. Then if not, buy some new cats, O2s and go to an exhaust place.


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## Daddioman (Apr 19, 2007)

*Re: Fix check engine light from non OEM Catalytic Converter Audi A6 1999 2.8 (Funkatollah Insaney)*

Wow that really covers it clearly. The dealer told me the DTC light / error message is caused by my cat problem, and the cats are making that rattly tin sound, which confirms bad cats. But I will call them back and see what they say about the possibility of faulty ECU coding. 
So are the O2 sensors built into the OEM cats. IF not, do i necessarily have to replace them ? or is it just the custom mounting requires new with brackets I'm not trying to be overly cheap, I'm just trying to understand this. 
For example if I replaced the cats with straight pipe, getting rid of the "rattly tin" exhaust sound, I would be stuck with the DTC Light on. I assume no one has created a device (not worth it) to fool the ECU that the delta range on the O2 sensors is OK. Again I'm just trying to understand how it works. I'll go along with doing my part to cut down on emmissions, your idea to fix seems simple and cost effective. Thanks again.


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## Funkatollah Insaney (Aug 17, 2004)

*Re: Fix check engine light from non OEM Catalytic Converter Audi A6 1999 2.8 (Daddioman)*

There is a way around it, but it involves a resistor in the connector, I think. That's a big, I think.
Go to an online store like summitracing.com and look at the replacements cats that they sell. You'll see what the job will entail. Depending on the style/ shape of cat you get will determine what work would need to be done. I really wouldn't go to the dealer for this one, unless warranty is involved.
Check your vin on one of those "check to see if your car has an recall" sites. Then you'll now. The ECU bug was too tight a tolerance for the delta and the older a car got, the harder it was to achieve that range. The cats were fine, but the ECU was indicating they were not.


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