CODE P 0420

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CBOWMAN500
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I have a 2003 Chevy Tahoe 5.3 with 4x4 with over 117,000 miles. The SESshowed on the instrument panel for some time now and I had it scanned. Per the mechanic it showed the oxygen sensor between motor and cat convertor drivers side was bad. I replaced it and cleared all codes. For 2 days no problem at all until this morning when getting on the Freeway the SES light came on again. Now after scanning it shows code P 0420 " Catalyst System Efficiency Below Threshold". can someone tell me what steps I need to take to figure out my next course of action?
Jul 31, 2006 at 12:30 PM
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DEMEARSJR
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What kind of fuel have you been running. If it calls for the higher octane and you run the cheap stuff it will cause it to plug.
Have you been running the ethanol mix, and if you have, for how long.
I've seen octane booster help in some situations.
Jul 31, 2006 at 1:17 PM
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CBOWMAN500
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Thanks for the reply. Same brand Mobil/ Exxon out here in Southern California. Nothing different regarding gas.
Aug 1, 2006 at 11:02 AM
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CBOWMAN500
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Problem fixed, dumped a bottle of fuel injector cleaner when I filled up and light went away, checked no codes.
Aug 3, 2006 at 11:09 AM
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DEMEARSJR
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Might be only a temporary fix, but if you run that stuff through every once and a while it usually helps
Aug 3, 2006 at 8:36 PM
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CBOWMAN500
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Well guess what? After driving some 800 miles this code is back! Anyone have any ideals what to do next?
Aug 7, 2006 at 11:08 AM