Yesterday I removed the heat shield on my manifolds in preparation of header install next weekend. After I got them out I sprayed all nuts and o2 sensors with on blaster. I do disconnect the o2 sensor for removal of the heat shields and plugged them back in when I was finished. I did not think to disconnect the battery before I started. After every thing was sprayed I let the truck idle for about 10 minutes while I cleaned tools. When I got in my truck to leave I noticed that the check engine light is on. Again all I did was disconnect the o2 sensors and then plug them back in. Would this cause the light to come on? Or coincidence? I am new to the forum and am excited for my new header install and cajun b pipes and uprev. Thank to everyone heat which is where most of my research came from. Thanks for the assistance