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Check engine code P0420 on 04 Audi A4 1.8T Quattro

Check engine light came back on after cat was changed three months ago. Got diagnostic code of P0420 and want most inexpensive way to clear it.

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5 Suggested Answers

6ya6ya
  • 2 Answers

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Posted on Jan 02, 2017

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chalkymon
  • 9 Answers

SOURCE: Management light Cat problem code

You mentioned a non genuine cat being fitted. That in itself is not too much of a problem, however, non genuine oxygen sensors are. There is a huge difference in quality between the genuine article and cheep alternatives on the after market. I very much suspect your fault code has been tripped by such a replacement part. Exceptionally complex engine management control systems just cant recognise the electronic info thats being sent by non-gen sensors, so its a false economy to fit these. Also one thing to bear in mind for the future is to avoid using super market fuels. Its a common belief that all fuels are the same and it all comes from the same tankers, etc etc. This is absolute rubbish. Its like comparing a 20 year old single malt Scottish Whiskey with a Happy Shopper bargain blend. It may look the same, but there's simply no comparison. Prolonged use of these cheep fuels will produce long term running problems. Also dont forget, there are pre and post catalytic converter oxygen sensors on your car, so the bills can get expensive. Good luck

Posted on Jan 17, 2009

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emissionwiz
  • 76846 Answers

SOURCE: 1997 LINCOLN TOWN CAR - CHECK ENGINE LIGHT( code P430)

I think you will find the aftermarket Cat Conv. is the source of your problem, but without hooking up to the factory test equipment at my disposal at my Ford dealer this at best and educated guess based on 20 years of emission related work, I am a Ford certified master electronics technician

Posted on Jan 30, 2009

localwonder
  • 6784 Answers

SOURCE: Check Engine light on!!!!!

its the O2 sensor for sure. normally, its good practice to change the sensor when changing out the muffler and cat system. doing it all together will prevent the sensor from faulting.

Posted on Mar 11, 2009

  • 1 Answer

SOURCE: i have a 2001 Audi A6 quattro, 120k miles, check

i have a 2001 Audi A6 quattro 95,000 miles when i change gear the car seems to over rev or keep reving when i put my foot on the clutch for a split second chould you tell me why is this

Posted on Jan 27, 2010

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The brown wire from the downstream sensors is broken or otherwise not connected to the computer. Check for damage to the wire.


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I have a 2001 Audi A6 quattro, 120k miles, check engine light came on a few months ago and code said it was O2 sensor, this past week when i drive the car engine sounds really loud like it is revving...


i have a 2001 Audi A6 quattro 95,000 miles when i change gear the car seems to over rev or keep reving when i put my foot on the clutch for a split second chould you tell me why is this

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Check Engine light on!!!!!


its the O2 sensor for sure. normally, its good practice to change the sensor when changing out the muffler and cat system. doing it all together will prevent the sensor from faulting.

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1997 LINCOLN TOWN CAR - CHECK ENGINE LIGHT( code P430)


I think you will find the aftermarket Cat Conv. is the source of your problem, but without hooking up to the factory test equipment at my disposal at my Ford dealer this at best and educated guess based on 20 years of emission related work, I am a Ford certified master electronics technician

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