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post #1 of 2 Old 05-06-2009, 01:20 PM Thread Starter
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Question P0421 Code Problem, Please Help

I have a 2001 dodge stratus coupe.

My check engine light will be on for days and then it will go off for a day and then come back on for days. So I have taken it to 3 shops and got the diagnostic test done on it 3 times. All 3 times they told me the code was a
P0421 (warm up cat efficency low bank 1)

The first shop wanted to replace the 02 censors front and back. They could not confirm to me that it would fix the problem for sure it was just one step and it could fix the problem but it might be something else. SO it seems like to me they were just guessing at what the problem was.

The second shop told me that it was the catalystic converter that needs to be replaced. So that was something different from the first place. So I wanted to get one more opinion.

The third shop read the test gave me the code and said that they have another team of course for more money that could actually pin point the exact problem. Now I was thinking why was this test not just done in the first place then.

I have a couple questions.

First is there really another test besides the diagnostic test that could pin point the exact problem of this p0421 code problem.

Second I have been told that not fixing this problem will not cause any damage to my car and that I will just not be able to pass an e-check. Is this true?

Third is there a way or a tool I can buy to turn my check engine light off so that I can just pass the e-check and deal with the problem later if I needed too?

Thank you in advance for any help with my problem.
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post #2 of 2 Old 05-07-2009, 01:23 PM
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Most likely the catalyst material has deteriorated. To set the 0421 fault both upstream and downstream O2 sensors have to be indicating the same reading for a set of seven samples of 12 seconds each during warm up. To me this indicates that the O2’s are probably good & that they are working equivalent to one another. Typically with a good catalyst the upstream O2 will be reading the rich/ lean thing back & forth rather quickly. Meanwhile the downstream should be nice and stable in the middle ground indicating a functional catalyst. So if the O2 signals follow each other too closely then the catalyst is no longer effective & a fault is set. It won’t hurt the engine but it’s probably not going to pass the emission test.
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