2003 silverado 1500 5.3L gas with a P0420 code, inefficient catalytic bank 1... i have no other codes...what elso can I check , meaning what can i start testing to troubleshoot and repair this

Asked by Jun 07, 2014 at 12:42 PM about the 2003 Chevrolet Silverado 1500 Long Bed 2WD

Question type: Maintenance & Repair

im not burning oil, im not losing any coolant, it runs relativlely strong except at times it
runs a little rough.  what also can I check on ?  could you walk me thru the diagnostic
process to get my trucki back in shape?

2 Answers

59,025

Sounds like you need a new catalytic converter. You can check the downstream oxygen sensor(s) to be sure. Basically what sets this trouble code is when the computer (PCM) "sees" too much fluctuation in the exhaust gases leaving the catalytic converter. Faulty wiring for the downstream oxygen sensor or a bad downstream oxygen sensor can, occasionally trigger this trouble code. But if your Silverado has higher mileage on it I'm willing to bet the catalytic converter is worn out. HTH. -Jim

Po420 Bank 1 and Po430 Bank 2 is your upstream and down stream 02 sensors so just change those and erase code my scanner or battery post take off it will run rough miss some pulling a little while driving and maybe a couple other signs too.

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