# P0420



## cmrguitar504 (Feb 7, 2008)

Got a CEL the other day and code came up P0420. I searched and found that this is 02 sensor related... and some people have said you can clean the Mass Airflow Sensor to fix this. I'm an amateur when it comes to this kind of stuff so if somebody could answer the following questions I would really appreciate it.
By the way, car in question: 2001 VW Jetta VR6, spark plug wires replaced is the only engine modification
1. How much could I expect to pay to solve the problem, if it is an 02 sensor? I'm pretty sure mechanic said "right" bank?
2. Is there anything I can do to try and fix this myself before paying?
3. If I am able to fix it, will the CEL turn off? Or does that all need to be reset?
Please don't flame me if I'm asking stupid questions. Thanks to anybody that can help! 

http://****************.com/smile/emthup.gif


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## cmrguitar504 (Feb 7, 2008)

*Re: P0420 (cmrguitar504)*

ttt... help


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## Dave928 (Feb 11, 2000)

*Re: P0420 (cmrguitar504)*

did you read the 3rd post from the top in this forum?


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## dana vw tech (Sep 20, 2005)

*Re: P0420 (Dave928)*

You may want to get your VIN checked for any open recalls. There is a specific update for the ecm related to your dtc.
This is a Vag-com forum specifically, so you may want to find a "Generic" forum or find someone with a system to give you a real scan. 
http://forums.vwvortex.com/zerothread?id=1260842
I am not blasting you, a generic scanner is ok for auto-zone parking lot diag, but worthless for most other repairs.
If you I/M me your vin, I will gladly check for recalls.


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## vr6turboalluneed (May 8, 2006)

*Re: P0420 (cmrguitar504)*

p0420 is usually related to a cat issue but vey possible is also very related to vacuum leaks check with starting fluid


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## remmyGLI (Jan 17, 2008)

*Re: P0420 (vr6turboalluneed)*

there is a recall for this fault. the recall is known as the N8 recall. involves ecm reflash and possible 02 sensor. call your local dealer, give them your vin and ask if any recalls are open. http://****************.com/smile/emthup.gif


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## cmrguitar504 (Feb 7, 2008)

*Re: P0420 (remmyGLI)*

thanks a ton to all of you. sorry i posted in the wrong thing... I had no idea. I'll be calling the dealer first thing tomorrow! :thumbup :


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## LoydKrissmas (Jun 28, 2005)

*Re: P0420 (cmrguitar504)*

It's actually the N7 recall.


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## remmyGLI (Jan 17, 2008)

*Re: P0420 (LoydKrissmas)*


_Quote, originally posted by *LoydKrissmas* »_It's actually the N7 recall.

Yup, my bad.


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## cmrguitar504 (Feb 7, 2008)

*Re: P0420 (remmyGLI)*

no recalls open for my car, unfortunately. http://****************.com/smile/emthdown.gif 
where do I go from here?


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## remmyGLI (Jan 17, 2008)

*Re: P0420 (cmrguitar504)*

Will need a cat to fix.


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## cmrguitar504 (Feb 7, 2008)

*Re: P0420 (remmyGLI)*

how do you know the cat's bad?


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## remmyGLI (Jan 17, 2008)

*Re: P0420 (cmrguitar504)*


_Quote, originally posted by *cmrguitar504* »_Got a CEL the other day and code came up P0420.:


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## LoydKrissmas (Jun 28, 2005)

*Re: P0420 (remmyGLI)*

try doing the spark plug arrestor trick...worked wonders on mine!


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## avduka (Aug 22, 2007)

mind sharing more info about the spark plug arrestor trick?
I got the same code on my VW Passat 2002
I need to pass NY inspection and I would like to get this code gone for good.
My mechanic was able to have me pass inspection by hooking up his VAG COM and playing around with it then sending me down the road to his people to pass..I have no idea what he did but would like to know so I can do it in future.
Any one know?


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## remmyGLI (Jan 17, 2008)

*Re: (avduka)*

spark plug arrestor takes the o2 sensor out of the exhaust stream so it does not get a correct reading. kind of like a diluted sample. most states do whats called an obd emissions test, which checks "rediness monitors". These are a self test for emissions components, and as long as they check ok, the vehicle will pass. my guess is what your mechanic did was set all of the monitors except for the cat, as most states can have 1 monitor not set.


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## vwemporium (May 27, 2002)

*Re: (avduka)*

DMV is aware of the diluted reading trick and if you get caught doing it or even having it in there to circumvent the monitors you could be fined not only by your state but a federal level.
The mere discussing this in a public forum is the most stupid admitting of liability I have ever seen.
Someone should black hole this.
Oh and the Cat must be one of the monitors that passes. In all states as it is the main requirement to passing.
You should check your air mass/air filter and verify your software level.
Then verify 01-04-046
There where many reflashs avaliable that where the legal way to rectify.
Best,
Jack


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## avduka (Aug 22, 2007)

I am not gonna do anything thats illegal..
How do I check the air mass/air flow filter? I ve read that many people got rid of this code by cleaning it really good..
Where is it located in the passat?
ooo and are there any reflashs available for the passat 2002 1.8t?
Thank you


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## nickg (Nov 11, 2001)

*Re: P0420 (cmrguitar504)*

make sure that your car has the updated flash that fixes the p0420....p0420 does not mean that the cat is definetly bad, it can be:
lazy 02
bad maf
carbon /deposit build up on t body or intake valves
electrical issue with engine harness or o2 sensers
i suggest youo do a top engine clean (gm top engine cleaner) to decarbon the engine and clean the cat itself (yea, gm top enginme cleaner will do that ), make sure the flash is up to date and then if it is not fixed look into a cat
if you do need a cat, make sure to fix what made it go bad...like the overfilled oil (big cause in VW btw), the bad valve stem seals , bad o2 sensers etc..and if you drove on bad wires for a while...you ruined the cat so you earned it









_Modified by nickg at 11:17 AM 12-2-2008_


_Modified by nickg at 11:20 AM 12-2-2008_


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## nickg (Nov 11, 2001)

*Re: P0420 (remmyGLI)*


_Quote, originally posted by *remmyGLI* »_Will need a cat to fix. 

not correct....it MAY need a cat


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## avduka (Aug 22, 2007)

sorry for my stupid newb questions but how do you make sure that you have the updated flash?


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## nickg (Nov 11, 2001)

you check the software version in the ecm...or call the dealer with your vin and see if there is a flash/recall available for your car...there should be


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## nickg (Nov 11, 2001)

https://www.edmunds.com/mainte...ip=#3
is a good read for you...look at line item 3

use the nhtsa numbers to view these on 
http://www-odi.nhtsa.dot.gov/tsbs/tsbsearch.cfm
10021950 is the latest in the emmissions/reflash updates


_Modified by nickg at 11:49 AM 12-2-2008_


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## cmrguitar504 (Feb 7, 2008)

*Re: (nickg)*

i've looked into everything mentioned here... it appears the ECM reflash was done in March 2008 (before I owned it). Already tried cleaning MAF, disconnected/reconnected battery and light stayed off for a week but came back on Saturday. What's the next step? I'm lost... any help is really appreciated. Thanks for everything you've done so far. http://****************.com/smile/emthup.gif 


_Modified by cmrguitar504 at 4:01 PM 12-2-2008_


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## nickg (Nov 11, 2001)

then you need a cat...


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## cmrguitar504 (Feb 7, 2008)

*Re: (nickg)*

what about 02 sensor?


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## nickg (Nov 11, 2001)

you need to look at their performance on an ocilliscope or graph...vag com can give you realtime data, but it sounds at this point to be the cat


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