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Code P0421

Tiny
ROBHAYNES84
  • MEMBER
  • 2004 DODGE STRATUS
  • 2.4L
  • V6
  • 4WD
  • AUTOMATIC
  • 193,000 MILES
I have already replaced my rear catalytic converter and downstream o2 sensor along with fixed exhaust leaks. MAP sensor and I know I have a valve gasket cover leak but I am still getting a p0421 code.
Friday, April 30th, 2021 AT 6:54 AM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

There is no 421 code. There is a 420 which I assume is the code. It is for the front cat converter. When you said you replaced the rear cat, what exactly did you replace?

https://www.2carpros.com/articles/catalytic-converter-replacement

I attached the diagram of the system and also the front or only cat converter for you.

If you have no exhaust leaks, it is the only possible failure. I attached some possibilities for you.

Roy
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Friday, April 30th, 2021 AT 11:07 AM
Tiny
ROBHAYNES84
  • MEMBER
  • 3 POSTS
Here is a list of everything I have had replaced: catalytic converter, MAP sensor, all exhaust leaks, and downstream o2 sensor. I do still have a valve gasket cover leak and still getting that p0421 code on my car listed above coupe.
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Friday, April 30th, 2021 AT 1:53 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Can you please verify the code? There is no 421 code listed.

Roy
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Friday, April 30th, 2021 AT 1:57 PM
Tiny
ROBHAYNES84
  • MEMBER
  • 3 POSTS
Code P0421 †Catalytic Converter Oxygen Sensor Below.
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Friday, April 30th, 2021 AT 2:36 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
What is the voltage reading on the downstream O2 sensor?

Is it steady or does it very?

Roy
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Friday, April 30th, 2021 AT 3:02 PM

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