# MIL and OBDII code P0421



## sonnybihis (Feb 4, 2009)

First of all I hope I'm in the right forum, sorry if I'm not. Hopefully I can get help anyways. I got a MIL on Saturday. It came up as P0421 Warmup Catalyst low threshold (Bank 1). I erased it and it didn't come back until today...maybe 250-300 miles later...when I took the car in for a smog check. The results of the smog check don't show any emissions out of spec so I'm assuming the problem is with an O2 sensor. Has anyone had any experience with these? Can this O2 sensor be removed/cleaned/replaced, or does it need to be replaced w/ a new one. Please let me know. Thanks!


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## sonnybihis (Feb 4, 2009)

I just found this...
http://www.vaglinks.com/Docs/A...e.pdf
i hope that's it!


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## ErockBar1 (Apr 12, 2005)

*Re: (sonnybihis)*

I threw a similar code on my old 1.8t GTI. It was the O2 sensor in front of the cat. Got a new one from ECS tuning and swap it out myself. Took total of 20mins.


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## sonnybihis (Feb 4, 2009)

*Re: (ErockBar1)*

i'm hoping that it's that easy for me too if it's not the ECM thing above. the dealer told me that it would cost me $250 for them to update the ECM. i think it's wrong that they wanna charge me for something that's a known issue with that car, regardless of it's age...


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## 2002a642 (Nov 30, 2008)

That update may fix the problem but it may have been done already and more then likely its the catalyst not the o2


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## b5in (Sep 10, 2003)

*FV-QR*


_Quote, originally posted by *sonnybihis* »_i'm hoping that it's that easy for me too if it's not the ECM thing above. the dealer told me that it would cost me $250 for them to update the ECM. i think it's wrong that they wanna charge me for something that's a known issue with that car, regardless of it's age...


I have a 2001 as well & that fixed my exact problem, although my dealer only charged me $180. I made the same complaint, since they said themselves that the parameters were set too sensitive from the factory so why should I have to pay, but in the end I had too in order to get my car back


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## sonnybihis (Feb 4, 2009)

*Re: FV-QR (b5in)*


_Quote, originally posted by *b5in* »_
I have a 2001 as well & that fixed my exact problem, although my dealer only charged me $180. I made the same complaint, since they said themselves that the parameters were set too sensitive from the factory so why should I have to pay, but in the end I had too in order to get my car back

i'll cross my fingers then...i found another dealer that will only charge me $120...and yes, it's bs that audi would charge customers for problems caused by them!


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## sonnybihis (Feb 4, 2009)

*Re: FV-QR (sonnybihis)*

the update worked! i used a friend's vag-com to check the software version before the flash, then asked for the printouts of the old and new software version page (see tech bulletin) to make sure they actually did something. hope this helps someone else!


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