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CODE P 0420

Tiny
CBOWMAN500
  • MEMBER
  • CHEVROLET
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?
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Monday, July 31st, 2006 AT 12:30 PM

5 Replies

Tiny
DEMEARSJR
  • MECHANIC
  • 110 POSTS
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.
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Monday, July 31st, 2006 AT 1:17 PM
Tiny
CBOWMAN500
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  • 4 POSTS
Thanks for the reply. Same brand Mobil/ Exxon out here in Southern California. Nothing different regarding gas.
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Tuesday, August 1st, 2006 AT 11:02 AM
Tiny
CBOWMAN500
  • MEMBER
  • 4 POSTS
Problem fixed, dumped a bottle of fuel injector cleaner when I filled up and light went away, checked no codes.
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Thursday, August 3rd, 2006 AT 11:09 AM
Tiny
DEMEARSJR
  • MECHANIC
  • 110 POSTS
Might be only a temporary fix, but if you run that stuff through every once and a while it usually helps
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Thursday, August 3rd, 2006 AT 8:36 PM
Tiny
CBOWMAN500
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  • 4 POSTS
Well guess what? After driving some 800 miles this code is back! Anyone have any ideals what to do next?
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Monday, August 7th, 2006 AT 11:08 AM

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