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Unread 11-30-2008, 07:12 PM   #1
Kiwi Jeeper
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OBD Code P0420(M) - possible causes?

I have had my cat converter and front O2 sensors replaced last year (about 12 months ago). Since then I have driven about 12k kms.

This weekend I got the check engine light and the code that has come up is P0420(M) - catalyst converter efficiency below threshold.

What could be causing this? Surely an O2 sensor or cat converter can't go bad in about 12k??? TJ has done 94k kms total.

I did clear the code and it hasn't come back this afternoon (only driven for like 5 kms).

I wanted some ideas before throwing money replacing parts. Thanks.

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Unread 11-30-2008, 07:55 PM   #2
durango-bob
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That would be the rear O2 sensor.
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Unread 11-30-2008, 08:36 PM   #3
ktroth
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umm like it says unfortunatly cat or 02 sensor
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Unread 11-30-2008, 08:38 PM   #4
Kiwi Jeeper
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Quote:
Originally Posted by durango-bob View Post
That would be the rear O2 sensor.
Thanks. Looks likely given that it was not changed (everything else was changed in the exhaust starting from cat converter and back).
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Unread 11-30-2008, 08:40 PM   #5
Kiwi Jeeper
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Quote:
Originally Posted by ktroth View Post
umm like it says unfortunatly cat or 02 sensor
I was looking for an "AND" answer

Don't want to change both (and spend unnecessary $$, in case only one is busted). The question was more around which one of the components is more likely to be the cause.
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Unread 11-30-2008, 08:47 PM   #6
ktroth
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if the rear o2 sensor was not replaced then that must be the culprit. it sucks. its a trial and error system. if its not one thing then its the other. good luck chasing the problem.
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Unread 01-27-2009, 10:34 AM   #7
johnk667
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P0420 Code

Hello, I am having the same check engine light code P0420. Did you ever find what the problem was?
john
03 Rubicon

Quote:
Originally Posted by Kiwi Jeeper View Post
I was looking for an "AND" answer

Don't want to change both (and spend unnecessary $$, in case only one is busted). The question was more around which one of the components is more likely to be the cause.
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Unread 03-06-2009, 03:53 PM   #8
saintv90
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I got the same error on my 04 Grand cherokee. I assume it's a o2 sensor...actually I hope it's an o2 sensor.
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Unread 03-07-2009, 01:51 AM   #9
Kiwi Jeeper
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In my case it turned out to be improperly done up gas tank cap. I don't know how that told the computer about cat efficiency. But it has not come back again, and I have not changed anything.
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