Code p0421

2004 DODGE STRATUS

193,000 MILES • 2.4L • V6 • 4WD • AUTOMATIC

ROBHAYNES84

MEMBER
3 POSTS

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.

Apr 29, 2021 at 11:54 PM

ASEMASTER6371

✓Experienced Mechanic
52,796 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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Apr 30, 2021 at 4:07 AM

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.

Apr 30, 2021 at 6:53 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

Can you please verify the code? There is no 421 code listed.

Roy

Apr 30, 2021 at 6:57 AM

ROBHAYNES84

MEMBER
3 POSTS

Code P0421 – Catalytic Converter Oxygen Sensor Below.

Apr 30, 2021 at 7:36 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

What is the voltage reading on the downstream O2 sensor?

Is it steady or does it very?

Roy

Apr 30, 2021 at 8:02 AM

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