Go Back   AudiWorld Forums > Audi Models > Audi A4 > A4 (B6 Platform) Discussion
Sign in using an external account
Register Forgot Password?


A4 (B6 Platform) Discussion Discussion forum for the B6 Audi A4 produced from 2002-2005

Possible Solution for Catalytic Converter fault codes - P0421 & P0431

Reply
 
 
 
 
LinkBack Thread Tools Search this Thread Display Modes
Old 12-09-2010, 01:04 PM   #1
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default Possible Solution for Catalytic Converter fault codes - P0421 & P0431

I was told something interesting that may save some of you a lot of money. I have a 2002 A4 3.0Q that I took into my local dealer (Cutrubus Audi/VW) for a CEL. I already knew what the fault was because I had it read at an Autozone where my brother works. It was a bad Cat and the code was P0421. I took it to my dealer this morning to take advantage of the federal warranty of 8 years/80,000 miles on emissions components so I could save money. As it turns out, the warranty applies to the in-service-date of the car which, for mine, was in February so the warranty expired ten months ago. When they ran the diagnostic they got two fault codes, one for each cat, but the readout said that each cat was below efficiency INTERMITTENTLY instead of being constant. When the service adviser saw this, he said that before I shell out $2000 for the repairs, I should buy an additive called '44K' and run it through the next two tanks of fuel. He gave me this speech about fuel quality and that I should only run 91 octane or higher and that I should only get it from an Audi-approved list of fill stations (i.e. Chevron, Conoco, Phillips 66, Texaco, etc.). I always run 91 octane or higher in all of my cars but I do buy it from a cheap supplier. Apparently, buying high octane fuel from 'lesser' brands/companies puts my car at risk for deposits and carbon build-up because of a "lower concentration of detergent additive in their gasoline" according to a letter AoA had sent to my dealer. My CEL could be what Audi calls a "false positive" meaning the computer thinks something is wrong when there isn't. The 44K additive is supposed to clean the gunk out and the CEL shouldn't come back. Don't know if anyone else has done this but I'm going to try it. I'll keep you guys posted.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-09-2010, 08:30 PM   #2
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default Update: erratic fuel gauge behavior

So later today, I noticed my fuel gauge was acting strange. The dealer cleared my CEL before I left but this time it came back on after driving less than 15 miles. When I drove out of the dealer lot, my gauge indicated a full tank and the range computer said I had 400 miles until empty. After driving approximately ten miles the fuel gauge showed a decrease of a quarter tank of gas and the range computer reads 305 miles to empty. Could these issues also be caused by poor fuel quality?
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-10-2010, 01:50 AM   #3
AudiWorld Member
Account #: 193353
 
jordonb's Avatar
 
Join Date: Oct 2010
Location: saskatoon, canada
Posts: 194
Default

yes.... poor quality fuels may have a higher concentration of sulpher and this builds up on the sender unit in the gas tank and gives wonky fuel level readings. i have seen this in both audi and vw.
i think what your dealer was referring to is "Top Tier" fuels, which are certified to be of a certain quality level determined by audi/vw and some other manufacturers

http://www.toptiergas.com/

i think they are right, get your min 91 oct fuel from one of the companies listed here

http://www.toptiergas.com/retailers.html

for the fuel level indicator issue, try adding a bottle or two of techron in each of your next couple tanks of fuel and see if it helps (i have heard it does help some ppl)
jordonb is offline   Reply With Quote
Old 12-12-2010, 08:01 AM   #4
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default Update after adding BG 44-K

I added a can of 44-K to a full tank of fuel yesterday and drove about 200 miles. The CEL has not cleared itself though I doubt it will anyway; I think it has to be done by computer. I have noticed that my MPG is starting to improve, but it could just be in my head.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-12-2010, 10:17 AM   #5
AudiWorld Newcomer
Account #: 175344
 
Join Date: Dec 2009
Posts: 8
Default

had the same issue, had a friend at an auto shop clear the light and have used 91/93 octane from sunoco ever since (not my first choice but the best option around) CEL never came back on 9 months and still running strong.
dj03 is offline   Reply With Quote
Old 12-12-2010, 06:48 PM   #6
AudiWorld Newcomer
Account #: 196810
 
Join Date: Dec 2010
Posts: 4
Default

or alternatively you can run ~ 2 cups of acetone per each 20g in the fuel tank and it should have a "cleaning" effect on your O2 sensors. (I wouldn't do it) i will just put in a new cat and be done with it. 6 bolts to wrestle,l 2 O2 sensors R&R and in it goes. Going with the flea-bay lifetime warranty direct fit replacement..... any one used them before????

oh and before anyone starts trying to "educate" me on the "you get what you pay for" subject. There are only 2-3 washcoat suppliers in the world, and all have comparable quality control. I should know this as i used to design catalytic converters for an oem in the past.
Kid Talegas is offline   Reply With Quote
Old 12-13-2010, 05:13 PM   #7
Audiworld Junior Member
Account #: 196877
 
Audi Tek's Avatar
 
Join Date: Dec 2010
Posts: 14
Default

The fault will come back. They always do. 6 minutes or 6 months... doesn't matter.
Audi Tek is offline   Reply With Quote
Old 12-16-2010, 07:22 AM   #8
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default So I guess what they say is true...

If your Check Engine Light isn't on, you're not driving an Audi.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-17-2010, 08:00 AM   #9
AudiWorld Member
Account #: 67508
 
Join Date: Dec 2003
Posts: 135
Default

had the same codes. 1st time the dealer cleared and everything went back to normal. Car never ran any differently. 2nd time codes cleared after about 4 days. Original issue was about 6 months ago. So far so good.
supawyde is offline   Reply With Quote
Old 12-17-2010, 10:27 AM   #10
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default

So what did you do to fix it, anything? What did the dealer say about it? I need to run my second can of BG 44-K and then have the light cleared to see if it did the trick. Just out of frustration, I went and drove an 02 Lexus GS430 to see if it would make a good replacement for my A4. There's no doubt it would be more reliable than the Audi but it was just so sedate and boring. Afterwards, driving home I could really tell how much fun the A4 can be and how it's the little things that make it so much better to drive. It would be really hard to sell it. An Infiniti G35 would come close but they lack so much refinement.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-20-2010, 10:12 AM   #11
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default

My CEL cleared itself today, Yahoooooo!!!
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-25-2010, 07:58 AM   #12
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default Update

Eversince my CEL cleared, I've been getting pretty crappy fuel economy. With the light on I would average 23-24 mpg mixed city/highway and that is calculated by hand. Now I will be lucky to get 20 mpg. I've not yet run the second can of BG 44-K through a tank of gas but I was wondering if this is normal.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-25-2010, 06:07 PM   #13
AudiWorld Member
Account #: 193353
 
jordonb's Avatar
 
Join Date: Oct 2010
Location: saskatoon, canada
Posts: 194
Default

Well, I have a 1.8T, so I can't say what your mileage should be, but I don't think it should have dropped off.... Did you
change your brand/grade of fuel? Are you using ethanol blended gas? Is it possible you fouled your spark plugs?
jordonb is offline   Reply With Quote
Old 12-25-2010, 07:23 PM   #14
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default

I switched to Chevron 91 octane and I believe all of our filling stations in Utah have 10% ethanol fuel. I don't understand how I could have fouled my spark plugs and not have a misfire or rough idle.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-26-2010, 09:05 AM   #15
AudiWorld Member
Account #: 193353
 
jordonb's Avatar
 
Join Date: Oct 2010
Location: saskatoon, canada
Posts: 194
Default

Shell v-power 91 octane contains no ethanol.
If even your plug gap is incorrect it could affect performance without throwing a code. Not saying this is a guaranteed problem, but if you had some bad gas, maybe the plugs got a little fouled. for that matter, have you changed your fuel filter? I just changed mine a few days ago.... Quick and easy (maybe 20 minutes or less).Also, how is the air filter? Also check the little screen where air passes into the airbox to be sure it is clean and free of debris. Also, keep in mind that at this time of year with colder weather and snow on the roads that fuel mileage will suffer a little. Also, if you recently changed tires it could affect mileage.
Do you happen to have a vag com? It is a great tool for helping to diagnose problems.
jordonb is offline   Reply With Quote
Old 12-26-2010, 04:09 PM   #16
Audiworld Junior Member
Account #: 188355
 
A84Nate's Avatar
 
Join Date: Jul 2010
Location: Northern Utah
Posts: 64
Default

Thanks for the tip on the Shell V-Power but I'll have to search online for the nearest Shell station because we don't have many of those. I havn't changed any filters or my engine oil because I wanted to run a second can of BG 44-K through first to get things extra clean. My air filter is in good condition but I'm not sure about the other screen you mentioned. I did put a new set of tires on a few weeks ago and both my front and rear alignment done the same day. The all season tires I picked shouldn't be the culprit because they have a low rolling resistance. Today, after church, I noticed the smell of burning oil briefly while driving but everything else was normal. No smoke, warning lights, visible oil leakage, or odd smells coming from outside the car. May have been coming from the snow blower a man was using as I drove by.
__________________

It's not a real man's car if there is no stick to play with.
2002 Audi A4 3.0 6-speed Quattro
Goodwood Green w/ Beige Interior
Mods:AUX input
A84Nate is offline   Reply With Quote
Old 12-26-2010, 07:43 PM   #17
AudiWorld Member
Account #: 193353
 
jordonb's Avatar
 
Join Date: Oct 2010
Location: saskatoon, canada
Posts: 194
Default

again, not sure about the 3.0 engine, as i have a 1.8T, but i had an occasional oil burning smell too. it went away when i changed the valve cover gasket. if it wouldn't have gone away, i would have thought cam seal.
not sure how any of this might relate to your mileage dropping though... still, like i said, perhaps it is due to the winter weather and roads?
when you do get around to changing your oil, perhaps it would be a good idea to pull your plugs and inspect them (or for peace of mind, just install a new set).... any time i buy a new car, i do a seafoam treatment, change the oil, all filters, plugs, flush the brake fluid, and give it a real good overall inspection just so i know where some of the maintenance is at.
jordonb is offline   Reply With Quote
Old 12-27-2010, 05:54 AM   #18
AudiWorld Newcomer
Account #: 196810
 
Join Date: Dec 2010
Posts: 4
Default

Quote:
Originally Posted by jordonb View Post
again, not sure about the 3.0 engine, as i have a 1.8T, but i had an occasional oil burning smell too. it went away when i changed the valve cover gasket. if it wouldn't have gone away, i would have thought cam seal.
not sure how any of this might relate to your mileage dropping though... still, like i said, perhaps it is due to the winter weather and roads?
when you do get around to changing your oil, perhaps it would be a good idea to pull your plugs and inspect them (or for peace of mind, just install a new set).... any time i buy a new car, i do a seafoam treatment, change the oil, all filters, plugs, flush the brake fluid, and give it a real good overall inspection just so i know where some of the maintenance is at.
Another burnt oils smell case here. had me very worried until it went away once i changed the cabin air filter(!?). i checked around the valve cover and rear main as a local indie turned me on to it as typical seeping paths but my 1.8T is clean there....


also another vote for the wintery driving conditions and blended fuels to be a cause for your MPG drop. i am averaging 20mpg city and 28-29 mpg highway driving (at 80 mph averagish)..
Kid Talegas is offline   Reply With Quote
Old 12-30-2010, 07:38 PM   #19
Audiworld Junior Member
Account #: 195189
 
Join Date: Nov 2010
Posts: 37
Default

Where did you get this 44K? I want to try it.
wheelmanbg is offline   Reply With Quote
Old 01-03-2011, 03:36 PM   #20
Audiworld Junior Member
Account #: 44360
 
Join Date: Oct 2002
Posts: 95
Default

Yeah, I might want to try it too. I have the same issue for one of my cats on my 8 yr old 3.0. I was a couple of thou over 80K, so no coverage. Unfortunately, my guess is that the code will come back some time in the next few mos. My light has gone off but it always come back. Fixing the cats under CA law is cost prohibitive, unfortunately. You may have the option of a cat bypass or a non-CA legal cat, either of which would cost much less than a replacement.
Trey A4 is offline   Reply With Quote
Old 01-03-2011, 03:36 PM
AudiWorld
Audi R8




Paid Advertisement
 
 
 
Reply

Tags
2001, 2002, 30, a4, a6, audi, catalyst, catalytic, code, converter, fail, forum, p0421, quattro, troubleshooting, v6


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



Join AudiWorld

All times are GMT -8. The time now is 09:07 PM.


Copyright 2014 AudiWorld.com Audi Enthusiast Community