2002 GMC Sierra Codes

I have recently had two codes come up on my truck for the catylatic converter being clogged up, and I had the pipe taken off and everything taken out too make a straight pipe, with the oxygen sensors still in. The two codes are now gone but there is a new one coming up P0420 which also has too do with the converter. I was wondering what I could do too fix this, or a way to get the service light off for this code without putting on new converters??

Your truck has O2 sensors before and after the cats, the sensors after the cats are designed to make sure that the cats are working correctly. With the cats gone the rear sensors are not reading where they are suppose to and tripping the code. There are two ways to fix the problem, one (the legal way) is to put new cats back on, look in to high flow cats, two (the illegal way) to buy O2 sensor emulators that plug in to the wire and trick the computer in to thinking that the cats are working, you can buy them from summit racing. Keep in mind that removing the cats is against federal law.

Remove cats=federal offense!