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2002, audi, code, po421

Help with code - P0421... already STFA

Bob 2KS4 on 10-09-2008

10-18-2022 11:16 PM
by AmreDiora

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3

8,565

S4 / RS4 (B5 Platform) Discussion

a6, audi, p0421, po421

fixed 16805 P0421 with O2 extender

johnkk on 09-22-2013

09-22-2013 06:46 AM
by johnkk

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0

2,492

A6 / S6 (C5 Platform) Discussion

02, 2002, 2004, 30, 30v, a4, audi, avk, b6, check, code, coils, engine, light, mileage, misfire, p0421, po421

P0421 and misfires 04 A4 3.0

blueskymine on 09-14-2012

09-20-2012 01:57 PM
by ct_esq

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2

3,738

A4 (B6 Platform) Discussion

2002, 30, a6, audi, catalyst, code, coils, efficiency, ignition, po102, po172, po175, po421, quattro, tt, warm

2003 3.0 Engine and ESP lights on (P0102, P0172, P0420, P0421)

IbizaKiwi on 08-29-2011

08-30-2011 10:10 AM
by IbizaKiwi

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2

8,453

A4 (B6 Platform) Discussion

2002, 2003, 27t, 30, a6, allroad, audi, catalytic, code, codes, p0421, p0441, po421, quattro

catalytic code

host23age on 11-19-2010

03-23-2011 01:56 PM
by ryan_qttro

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3

3,379

30v V6 Discussion

air, audi, injection, p0421, p1411, p1423, po421, s4, secondary

P0421 and other MILs

2000_A6_2.8_Avant on 11-19-2010

11-19-2010 04:54 PM
by 2000_A6_2.8_Avant

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0

1,507

A6 / S6 (C5 Platform) Discussion

2004, 27t, a6, audi, cat, clear, code, delete, engine, p0421, po421, replacement, s4

P0421 - Cat code

greenquattro on 05-01-2010

05-01-2010 06:34 PM
by VONBOTTLE

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1

2,376

A6 / S6 (C5 Platform) Discussion

0421, 2002, 2003, a4, a6, audi, check, code, engine, fault, light, p0421, po421, s4, trouble

Fault code 0421 comes on intermittently

robbellbottom on 12-12-2009

12-12-2009 07:34 PM
by Dana @ Ross-Tech

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1

1,595

VAG-COM Discussion

a4, a8, audi, b5, b6, borla, check, engine, exhaust, fixed, light, po421, po431, s4, s5

borla Exhaust

blacks42000 on 07-15-2009

07-20-2009 09:30 PM
by Tifosi

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6

1,499

S4 / RS4 (B5 Platform) Discussion

2000, a4, audi, code, fault, po421, road, rough, s4, sensor

02 sensors

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Multi-page thread

1 2)

blacks42000 on 05-17-2009

05-24-2009 03:07 PM
by blacks42000

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14

2,532

S4 / RS4 (B5 Platform) Discussion

16805, 20002, 30, 30l, a4, a6, audi, cats, giac, p0421, p0431, po421, s4

Looks like I need either both O2 sensors replaced or both Cats replaced.

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Multi-page thread

1 2)

A4AdMan on 03-01-2009

04-21-2009 12:45 AM
by diagnosticator1

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16

4,142

A4 (B6 Platform) Discussion

16815, 2000, 2002, audi, bad, catalytic, cel, code, codes, emissions, labree, p0421, passat, po421, po431, signs, vw

Catalytic converters gone bad

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Multi-page thread

1 2 3)

vmels on 12-09-2008

12-09-2008 01:55 PM
by 4Driver4

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26

5,262

A4 (B5 Platform) Discussion

2000, 2001, 2003, 27, 27t, a6, allroad, audi, catalytic, code, converter, engine, p0421, po421, quattro

2000 Audi A6 2.7T Quattro 90k miles P0421

upops on 07-17-2008

07-17-2008 06:34 PM
by i-DAR

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2

1,679

A6 / S6 (C5 Platform) Discussion

01, 27t, a6, audi, cat, catalytic, code, converter, dtc, indicator, lamp, malfunction, p0421, po421, thresold, vag

P0421 Code - Cat Or Sensor ?

Kirill on 03-19-2008

03-19-2008 04:59 PM
by Kirill

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5

5,479

A6 / S6 (C5 Platform) Discussion

1999, 2003, a4, audi, cat, code, mazda, miata, passat, po421, po431, po441, v6, vw, warm

Dealer suggests cat replacements, any suggestions?

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Multi-page thread

1 2)

Topexec on 01-09-2008

01-10-2008 08:52 AM
by KIWINI-RI

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12

1,489

A6 / S6 (C5 Platform) Discussion

2001, audi, cat, catalyst, failure, po421, s4, warm

Got a cel for PO421, Warm up catalyst below threshold...bad cat? bad 02?

Onebad S4 on 11-12-2007

11-12-2007 11:20 AM
by Vier GlÃ¼hende Ringe

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2

873

S4 / RS4 (B5 Platform) Discussion

2004, a4, a6, allroad, audi, auid, check, code, engine, main, obd, p0421, p0431, po421, s4

p0421 and p0431 codes

Brattleboot on 09-08-2007

09-08-2007 09:30 PM
by CTA4AVANT

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1

2,711

30v V6 Discussion

16805, audi, bank, catalist, code, effisioncy, p0421, po421

P0421/16805: Warm up catalyst efficiency below threshold, bank 1...

PSUEng on 01-19-2007

01-21-2007 06:59 AM
by 87ninefiveone

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3

2,091

S4 / RS4 (B5 Platform) Discussion

audi, p0431, p1555, po421

Now that I have a key to the kingdom.....not sure I want it!

jfk92 on 12-08-2006

12-08-2006 01:53 PM
by jfk92

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3

687

A6 / S6 (C5 Platform) Discussion

001, 02, 2002, 2004, 30, a4, audi, bad, code, fix, high, o2, oxygen, p0421, po421, sensor

P0421 code for O2 sensor

Kev 3.0 on 10-24-2005

10-25-2005 09:38 AM
by Kev 3.0

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8

3,149

A4 (B6 Platform) Discussion

27, 3510, a6, audi, dakota, diagnostics, p0421, po421, vagcom

emission test question ....P0421....please read...tx

audi2.7audi on 06-14-2005

06-14-2005 09:52 AM
by 4Driver4

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4

862

A6 / S6 (C5 Platform) Discussion

16805, 16805p0421, 27, 27t, audi, cel, p0421, po421

2000 2.7T. CEL Code 16805 P0421

ecgarzone on 03-12-2005

03-16-2005 02:12 PM
by ecgarzone

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2

1,224

VAG-COM Discussion

2000, 2001, 421, a6, aude, audi, auto, code, codepo421, dtc, po, po421, quatro, quattro, s4, vag

code PO421?

woods4 on 08-05-2004

08-12-2004 06:22 PM
by Rally_nutcase_1982

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3

2,150

VAG-COM Discussion

218084, audi, injector, p0431, p1555, po421

I have 5 DTC's. Can you guys help point me in the right direction...

Scott W on 07-29-2004

07-29-2004 07:48 AM
by Scott W

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3

400

S4 / RS4 (B5 Platform) Discussion

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