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P0420 NIGHTMARE!!!!

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Old 12-22-2010, 09:37 AM   #1
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Default P0420 NIGHTMARE!!!!

P0420 NIGHTMARE!!!!
I have no other ideas on where to go with this. I practically changed every part that has to do with this damn code and have not received any type of relief. I mean granted I thank this website and everyone’s input to getting rid of this code, but still cant get it to go away. I don’t want to take it to the dealer because it would cost me a fortune and believe it or not im under budget from taking it to the damn audi dealership and having them charge me 180.00 as a diagnostic fee. So after doing long time research on this code on the internet, I have replaced the following:
Both o2 sensors
Spark plugs
Spark plug wires (Thank you audi for the recall on the wires)
Spark plug coils
Vacuum tube toward the rear of the engine that I found cracked.
Cat converter

I left the Cat for last since it was the most expensive part to replace and I broke down and went with the repair only to find out that a couple days later “Ding” f-in engine light comes back on to give me the same code – p0420 (Autozone reading). Damn this code right to hell!!! I also read on the possible outcomes that this code can be tripped by a leak in the intake, is there a way that I could possibly detect that? I would like to take pride and be able to fix my own car, hence the other reason why I didn’t want to take it into the stealership. I have a 2002 Audi A4 1.8T for those that might have a further solution. Im on my last leg here on trying to figure this out and im about to punch my dash if I see this check engine light any LONGER!! Lol. Can someone throw me a bone here.

Respectfully, Pissed off Audi owner.

Note: I don’t think I’ve gone more than a month without this engine light going off. Next car = NOT AN AUDI!!
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Old 12-23-2010, 03:09 PM   #2
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http://www.obd-codes.com/p0420 - read...

On the bright side, you performed alot of good maintainance.

Since you replaced your cat, I would try looking further up on the exhaust system. Maybe a leaking exhause manifold. Or a malfunctioning engine coolant temp sensor?

I haven't had any experience with this code, but it sounds like you replaced most of the big stuff, so I would start looking at the smaller things.
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Old 02-21-2011, 06:09 AM   #3
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Well after months of battling this “p0420” code I FINALLY found a solution to get rid of the check engine light after replacing part after part associated with this code. I was about to give up and hand over 1400.00+ to the Audi dealership until I ran across one more solution. I started reading on information concerning an O2 spacer for the second bank. This spacer I guess, gives the O2 sensor a gap so that the temperature coming out of the aftermarket catalytic converter reads within limits and “poof” engine light be gone!!! So once again I have to thank this site on saving me about $700.00 and some change. Took me a little to figure this one out, but the cat was initially on the quits. So if you guys are on the same troubleshooting boat with this code and you have done EVERYTHING in its power, give the O2 spacer a try. I bought it for 23 bucks off a german parts website. Now awaiting my next check engine light troubleshooting issue…lol.
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Old 04-26-2011, 03:11 PM   #4
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Quote:
Originally Posted by infamous107 View Post
Well after months of battling this “p0420” code I FINALLY found a solution to get rid of the check engine light after replacing part after part associated with this code. I was about to give up and hand over 1400.00+ to the Audi dealership until I ran across one more solution. I started reading on information concerning an O2 spacer for the second bank. This spacer I guess, gives the O2 sensor a gap so that the temperature coming out of the aftermarket catalytic converter reads within limits and “poof” engine light be gone!!! So once again I have to thank this site on saving me about $700.00 and some change. Took me a little to figure this one out, but the cat was initially on the quits. So if you guys are on the same troubleshooting boat with this code and you have done EVERYTHING in its power, give the O2 spacer a try. I bought it for 23 bucks off a german parts website. Now awaiting my next check engine light troubleshooting issue…lol.
Hey bro.

I'm having the same damn problem. Changed everything and still the same problem. Can you please email me the link with the part number to: monty007@shaw.ca I love this car but this is driving me absolutely crazy!!!!

Thanks in advance!!

EJ
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Old 04-28-2011, 04:04 AM   #5
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EJ,

Don’t even bother spending your money on the spacer. This solution went well for about a month and the p0420 code showed its ugly face again. I’m on the same boat as you as to driving this car off a cliff, but then again it’s paid off so I guess I’ll deal with the light. So what I did was I took it to where I had the cat put in and they ran a test on the whole emission system and they said they had no idea what was wrong since it looked like everything ran fine. So I went onto advancedautoparts.com and looked up a coupon code and got a code reader / eraser for 33 bucks and have it in my passenger seat pocket. I erase the code drive for about a week then it comes back on, so then I just erase it again for the convenience of not looking at that damn thing on my dash. It also gives me the comfort that it’s still JUST the p0420 code. I took it up to the Audi dealership to find out if they could diagnose it and they actually diagnosed it for free (What a shocker!!!). But they told me that it was the cat and they wanted twice what I originally paid for a new cat. So I told them where they could shove that cat. But anyway, I’m still looking for a solution since I’ve changed everything that had to do with that code and still get the check engine light. The only thing that I haven’t done was get the ECM flashed so that the new cat reads within tolerance (which I believe is the only thing left to do). But I don’t really want to spend 400.00 plus to have Audi do 10 min of work. So I just reset the code every time it comes up. $33.00 bucks on a code reader and I could use it on the wife’s car too if I have any problems. But I’ll tell you what, since I’ve owned the car I haven’t gone a month without that engine light coming on. So I’ll just wait till this thing blows up and then NEVER look in Audi’s direction AGAIN…. BMW here I come!
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Old 01-02-2012, 05:18 AM   #6
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Default Problem solved so far.

So I finally found a solution for this p0420 code that has been on my dash for almost a year. To recap I had a cat converter code go off, I replaced everything associated with this code to include the cat, o2 sensors, coolant sensor, cleaned the maf sensor, new head gasket, spark plugs, coil packs, etc. My last resort was to reflash the ECM at the Audi dealership. I went there and just requested the flash, which was about 180 bucks and a hour and a half on the labor. NO MORE check engine light for the past two weeks!!!! Hopefully it stays this way and I don't have anymore issues and my car seems to be running alot smoother.
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Old 01-10-2012, 05:42 AM   #7
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do you mean reset adaption values when you say reflash?
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Old 01-11-2012, 05:15 PM   #8
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Default PO420 code

I did not see your mileage in the postings, but this may apply...You may be covered under 8 years or 80,000 miles (EPA’s Federal Emissions Law of 1995)if your CAT failed. I don't know what recourse is available to you now - but worth investigating. I had CAT replaced for free at Audi, but had to "remind" them of this coverage. I rack up a lot of miles each year so this was done a few years ago on my car - had it done at 79,000 miles. Also, I am not original owner of car - this does not matter under coverage.
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Old 01-12-2012, 05:18 PM   #9
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funny i saw this, started reading, was going to say there is a software update for too sensitive of converter failure codes. But i see you went to the dealer and had it done
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Old 01-16-2012, 04:09 AM   #10
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Outback,

I dont know the specifics behind what software that Audi had used, but i just let them know that i had changed the Cat converter and needed a reflash. They took care of the rest. I assume that they knew what i needed done as far as the reflash went.
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Old 01-16-2012, 04:17 AM   #11
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Pennac,

I was way over mileage for my cat to be covered under its warranty. Trust me I checked every solution to fix this before spending the money on a cat converter. i was up to 99K miles when the check engine light came on, so i figure i was due for the cat coverter. I couldnt find a way to get rid of the code until i came across an article on the sensitivity of the check engine code and how the ECM needed a reflash, problem solved......FINALLY!
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Old 03-12-2012, 05:40 PM   #12
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Quote:
Originally Posted by infamous107 View Post
Pennac,

I was way over mileage for my cat to be covered under its warranty. Trust me I checked every solution to fix this before spending the money on a cat converter. i was up to 99K miles when the check engine light came on, so i figure i was due for the cat coverter. I couldnt find a way to get rid of the code until i came across an article on the sensitivity of the check engine code and how the ECM needed a reflash, problem solved......FINALLY!
Does anybody happen to know if the REFLASH is available for the 2.8 motor? im getting a intermittent p0420 and an intermittent code for pre cat 02 sensor bank 1. i have a 01 a6 2.8 fwd. i would like to get this reflash so i can get rid of the code. (no MIL just stored code)
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Old 10-02-2013, 05:31 AM   #13
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Default Bad news....

My check engine light came back on after the reflash. So now I officially have NO idea what the hell is going on with the P0420 code on this car. It does happen as i drive for long periods of time meaning on long stretches of road without stopping. Thinking that the O2 sensors are reading a high temperature and then throws the code. Been trying a trial and error approach as I've been resetting the code with my code reader and finding out when the check engine light comes back on. I'm REALLY trying to avoid the Audi dealership as we're all trying to save a penny here and there now a days. I've changed a lot of items pertaining to this code as stated before. The only thing I could think of is 2 of my spark plug coils are a different brand than from the OEM replacements that I put in there since I had two burn up on me. Any help please!!!!
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Old 10-06-2013, 03:54 AM   #14
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Default Found another solution

I did another inspection on the cat that was replaced on my car while the car was in my garage. I plugged both exhaust with a rag and made a heavy soapy mix in a squirt bottle. I turned on the car and doused the cat with the soapy mix. Found that there was a crack in the weld of the cat. I assume that this crack is taking In an influx of O2 into the cat and giving the sensors a bad reading. Getting the cat replaced under warranty since it was put on recently (within a year). Here's to really hoping that this is going to get rid of the CEL p0420 code that has been haunting me for almost a year! I'll repost in another couple weeks with the outcome.
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Old 10-10-2013, 01:50 PM   #15
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What a nightmare?

I was going to ask if your "new" O2 sensors were exact bosch OE replacements or generic? I've had problems with 75% of the non exact OE aftermarket O2 sensors I've purchased; typically a "heater circuit" error but none the less, gernerics seem problematic in VW/Audi, both 4 and 6 cylinder.
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Old 10-14-2013, 11:14 AM   #16
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What a nightmare?

I was going to ask if your "new" O2 sensors were exact bosch OE replacements or generic? I've had problems with 75% of the non exact OE aftermarket O2 sensors I've purchased; typically a "heater circuit" error but none the less, gernerics seem problematic in VW/Audi, both 4 and 6 cylinder.
Hey Mark,

The O2 sensors were the Bosch OE replacements bought from an audi authorized dealer for VW/Audi cars. So unless they are at fault (even after a good voltage reading) I wouldn't have a doubt. But thanks for advice. Should have the new cat put on sometime this week. Hopefully it cures this damn light.
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Old 09-02-2014, 11:54 AM   #17
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Have you find any solutiins for this?
I bought recently A6 Avant with ARS engine (4.2 V8), after 1500miles i get P0430 with every 300miles. 1st i used OBD2 reader, but today i got VCDS(VAG-COM) and there is 2 faults now:

2 Faults Found:
16814 - Catalyst System; Bank 2
P0430 - 35-00 - Efficiency Below Threshold
17584 - Bank1: O2 (Lambda) Correction Behind Catalyst
P1176 - 35-00 - Control Limit Reached
Readiness: 0000 1001

I captured some data from O2 sensors, bank 1 sensor 2 seems to be dead, or getting lot of air..


Click the image to open in full size.

ASG 4.2 V8 juniku O2 sensor P0430 P1176



400miles before problems started, i started to use Shell V NitroPower instead of RE95, i dont know did it have anything to do with it, but next fill-up will be RE95, i will take car to to emission tests in early next week.

Last edited by Juniku; 09-20-2014 at 12:14 PM.
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Old 09-02-2014, 11:54 AM
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