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codes?


 
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stewart42
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Joined: 03 Dec 2005

PostPosted: Wed Aug 29, 2007 11:08 am    Post subject: codes? Reply with quote

Hi all
I have a 1996 4.0L grand cherokee - can anyone help with my codes? Using my OBD2 reader I get P0138 which is I believe the O2 sensor after the Cat. But when I do the key on/off I get codes 12,21,55. So does anyone know why the OBD2 reader only shows one code instead of two? What do you think the 12 & 21 codes mean? And lastly does the O2 sensor after the cat matter?
thanks
stewart
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kaos
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Joined: 10 Jan 2006
Location: Iceland

PostPosted: Wed Aug 29, 2007 3:51 pm    Post subject: Reply with quote

You can find the codes at http://jeephorizons.com/phpbb/viewtopic.php?t=2719.

P0138 is indeed O2 sensor #2.
12 is "battery or computer recently disconnected", 21 is O2 sensor, and 55 is end of codes. So both methods agree.

As for running without the downstream O2 sensor, I don't think it matters much. As I understand it, it is the upstream sensor that is used to correct the fuel mixture, and the downstream one is mostly there to check that the cat' is doing it's job. Please somebody correct me if I'm wrong. Of course, you might fail smog check and/or inspection if it's not working.

Best regards,
--
Kári
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viper24242
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Joined: 08 Jul 2005
Location: Harrisonburg, VA

PostPosted: Thu Aug 30, 2007 3:13 pm    Post subject: Reply with quote

Sounds right, from what I understand the #2 O2 senor is just to check to make sure the cat is working correctly. From what I understand in virginia if you have a check engine light on its an automatic fail. I would just replace it, the O2 sensors are pretty cheap.
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