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Old 08-29-2008, 01:33 AM
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Question A6 Catalytic (low activity) p0422 & p0432

A6 Quattro 1999: Low Catalytic Activity p0422 & p0432-
Background: 140,000 miles
1. Passed inspection here in NY, threw the first code about 50 miles later.
2. I just bought the car, last owner says the Cats were replaced about 5,000 miles back.
3. The car runs like a dream, but there are a couple of other things that aren't helping me diagnose this thing. Namely, the coolant temp sensor isn't reading on the dash (circuit broken?), and the digital screen that tells you engine efficiency and what gear your in is schizo (looks like it might be reading 18 mpg, or 10), but I can't tell the values until it's replaced.
4. I've turned the codes off (obdmeter), and they do come back about 50 miles later.

I understand that bad mileage could mean bad o2 sensors, and these should be replaced pronto. But I need the screen to work to prove low mileage. Don't drive enough to notice (NYC). Display replacement: parts or how do I do this? I need to know how to get the mechanic to diagnose this right so I don't replace cats and get the same code.

Any experience out there with this particular problem?
Could the temp sensor have something to do with it?

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Old 08-29-2008, 11:23 AM
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Join Date: Oct 2006
Location: Minneapolis, MN
Posts: 1,569

In order to fix the dash display you need to buy a replacement cluster for about $400.00. That is the only known working way I know of to fix it.

Your coolant temp sensor is more than likely bad, they are cheap and pretty easy to change yourself.

The o2/cats is out of my territory. I would contact the original owner and ask them to provide the shop name who changed the cats so you can verify there were in fact changed.

Sorry to hear you are having problems right away with your Audi. They are very common problems though. Assuming the cats have been replaced, this should be a cheap fix. I believe when the cats are bad it throws low flow/threshold codes, not activity.

Welcome to the forums.

'00 A6 Avant Quat 190k
50% Front 20% rear Tint
Euro Blindspot Mirrors / LED interior lighting
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Old 08-30-2008, 10:24 AM
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Join Date: Aug 2008
Posts: 2

Hey, thanks very much for the response Jeff.

I'm doing the coolant temp sensor today.

I will check the underside for any obvious sensor / cat issues.

I'm waiting for the seller to give me Cat replacement info. Unfortunately the code 0422 is a 'main catalyst below threshhold' code after taking another look. Hoping that means the cat replacement is still under warranty.

Question- if the cats are going bad, will I be doing any other damage to the car (or getting bad gas mileage) as a result of not replacing them immediately? The car isn't making strange noises, and seems to drive just fine.

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Old 09-13-2008, 03:49 PM
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Join Date: Sep 2008
Posts: 1

I have a similar problem. My code is P0421. My mechanic looked it over and told me to check with the Dealer as he believes the warranty was extended to 100,000 miles due to these types of problems. Does anyone know of extended warranties for catalytic convertors?
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Old 09-13-2008, 04:07 PM
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Join Date: Aug 2008
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I believe the warranty is 8 years/80k miles.
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Old 09-24-2013, 08:41 PM
1st Gear
Join Date: Sep 2013
Posts: 1

Hi the dash cluster is only $60.00 and you can replaced by yourself, or in fact take your cluster to a electronic repair shop to get it welded, the part is available online (ebay) be very careful a the time of the repair, part looks flexible but is metal veined and can be fragile a the welding time I replaced twice, search for instructional videos of how to disassemble the gauges, also the same problem still current in my vehicle with the codes P0422,0432,0300,0301,0303,0302,0134,0411 and again the same codes from p0300,0301,0302,0303, hope you resolve the dash problem, thanks.
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