P04X1 codes literally mean the o2 sensor is picking up less-than-perfect warm up catalytic converter performance. The thing is that earlier versions of the ECU software had very low threshold value programed. So even though the performance of the converters were acceptable as far as the emission requirements are concerned, CEL was triggered because the computer thought that the converter(s) were bad, even though it had good useful life left in them. The updated software revised the threshold so the CEL was not triggerd prematurely; however, that does not mean that all P04X1 codes are due to the software issue.

If the ECU software version is up to current, and CEL is being thrown, then it probably means that the converter(s) are in fact bad. The reason that many of us are telling people to check the software version is that it is cheaper to update the ECU than to replace the converters. The only issue is that the ECU flash is typically a dealer procedure.

You do have a good point though. I know for sure that reputable chip tuning guys will base their tune on the latest software. So theoretically, if you get your car flashed with one of these, and had the issue based on the software, you MAY get rid of the code. But if you get a tune that is based on the old software, and your car already had the dealer update, then it WILL trigger the P04X1. (I am the living proof.)

Just be careful when you are messing with the emission stuff, because it can be a headache.

 

I have the P0421 code for two weeks now.

So in summary, reflash/update the ECU at the dealer, and then get the the tuned chip?

I've read a few articles regarding symptoms of bad cat, well, I don't have any of the symptoms. My cat was replaced at 40k miles --now the car has 108k

 

Check for updated software on your ECU first. If the version is not, then update it.

There is no need for the tuned chip if you are doing the dealer update.

BTW, you can fowl up the converters in 60K miles. If you have VAGcom, then you can run through the converter efficiency tests.

 

Quick reply hxgaser. Thanks a lot.

How do I know my ECU has been updated?

How do I know I have a VAGcom?

Guys, excuse my ignorance. I am new to Audi's.

 

VAGcom is a diagnostic tool available from RossTech. It runs on a computer, preferably a laptop, through a usb to OBD II cable. You can buy a full version from Rosstech or get a limited version through ebay.

Once you have VAGcom, you can look up your software version of the ECU. I don't remember the latest version number, but I can look it up if you need it.

 

I have the same code (P0421 only) coming up on my 02, A4, 3.0/108k. I get 210mi from a tank which is averaging consistently to about 15MPG.

Everyone is saying that their cats are bad, but their gas is still the same as it was before. I bought this car like a month ago, and I was like WTF? How come the gas milage sucks so bad?

I am think that the O2 sensor has actually gone bad in my case.

I would really appreciate some feedback.

Thanks in advance, Igor

 

I have the same code (P0421 only) coming up on my 02, A4, 3.0/108k. I get 210mi from a tank which is averaging consistently to about 15MPG.

Everyone is saying that their cats are bad, but their MPG is still the same as it was before. I bought this car like a month ago, and I was like WTF? How come the gas milage sucks so bad?

I am thinking that the O2 sensor has actually gone bad in my case.

I would really appreciate some feedback.

Thanks in advance, Igor

 

You may have the front O2 sensor not working properly AND the cat as well. Front O2 has nothing to do with that code, but may have an impact on gas mileage. Try replacing the front O2 and see if there's any difference in fuel efficiency, at the same time reset the CEL.
However, used Audi may have hidden problems...

 

The CEL is the hidden problem. The guy before me would clear the codes every time he came to show the car to me. So I bought it and now I'm stuck trying to figure out what's wrong. But I get what you're saying.

So what you're trying to say is that I should be looking at a different O2 sensor to change for the MPG to get better or in fact the Bank 1(P0421)?

Igor

 

His suggestion is to replace the UPSTREAM (or front) O2 sensor on that bank (1) and see if that improves your gas mileage woes.
You could also check the spark plugs on that bank for fouling.
Both these items are the first things you can actually do something about'em without much wallet distress, before pulling the trigger on the expensive cat replacement.
The DTC code is thrown by the DOWNSTREAM O2 sensor (behind the catalytic convertor), signaling that there's efficiency trouble with the cat.