I checked my '03 trailblazer (4.2L) for codes and only 1 came up. It was a cylinder 2 misfire. I changed the plug, as well as, the coil. It runs great now. I tried to reset the SES light by disconnecting positive terminal from battery for a few minutes, as this worked after I changed the thermostat. That didn't work. I than checked manual and said to unplug pcm b and pcm I fuses and that didnt work either. Is there anything else I can try?
Did you read the codes again? Either the same code is setting or there's a different problem. If the code is for the same cylinder, try swapping the injectors between cylinder 2 and another one, then see if the misfire code moves to that cylinder. Also, there's always a long list of conditions that must be met for a code to set. One of those conditions is that certain other codes can't already be set. When there's a cylinder misfire code already there, some other self-tests won't run so those related codes won't be set. Once the cause of the misfire is solved, the self-tests will resume, then the computer may detect the next problem.