I have an Audi A4 Quattro with the 2.8L V6 engine. For some time, I've had an intermittent check engine light. More recently, the light is on basically all the time. When I read out the codes I get P0421 and P0431(warm up catalyst efficiency below threshold for both left and right banks). The car has 130,000 miles on it. The engine and exhaust system are stock. Drivability is the same as it always has been, as is my mileage. The engine uses some oil (three-fourths of a quart in 5000 miles). I have never had to add any antifreeze. So I have no reason to suspect the cats have been poisoned by anything.

I find it hard to believe both catalytic converters would fail at the same time without some common precipitating circumstance. I am wondering if there is some other sensor that is involved in throwing this failure code. As I checked through my maintenance logs I realized I never changed any of the O2 sensors. But if I had a bad upstream O2 sensor I would expect my mileage to be affected and I don't see that. Plus, I believe there are specific trouble codes for O2 sensors and I don't see those. Does the engine coolant temperature sensor enter into this picture? I know they fail fairly frequently for the dash temperature indicator. Since there are two elements in the one sender unit I wouldn't be surprised to see the other one that feeds into the ECM also fail.

Last week I had to wait 20 minutes to exit a parking garage and the next day my check engine light turned off. Then after a few more start/drive cycles it came back on. So idling for a while was able to clear the problem code. Does that suggest anything?

I would appreciate any suggestions. I have an annual vehicle inspection coming up and I really hope I don't have to replace both cats.

 

There is a engine control module update for 2000 and some 2001 models....

 

It's a 2000. The engine code is ATQ.

 

Sorry, I just noticed the body of your message, which is very interesting. Is this engine control module update just some new code that gets flashed into the ECM? Or are there some hardware changes involved as well (like a new ECM itself)? Does the update change some set-point or trigger values for determining the warm up catalyst efficiency? I suspect I know the answer to this question, but is this something my dealer will do for free (because it was a deficiency on Audi's part) or will I need to pay for the upgrade? I'm sure the cost of the upgrade will be a whole lot less than the cost of two cats.

 

Visit your local dealer and ask them if the IC service action has been performed to your vehicle, if not it should solve your catalyst efficiency code problems.

 

Carson,
I had the IC service action performed 5 days ago. Despite what Audi of America said my local dealer did not charge for this (my car is beyond the 8 yr/80K miles federal emissions limit). Since then the car has seen about 25 start/drive cycles and NO check engine light. Previously, the CEL had been on virtually continuously for months. So I'm just about ready to blow the whistle on this one.

I cannot thank you enough. For sure, the easiest and cheapest repair is the one you don't have to do! Your knowledge and willingness to share it certainly saved me some big bucks and a lot of aggravation. Thanks!!