2004 Chevy Trailblazer LS,V6, 4.2L. Service Engine Soon Light on. Where To Start

Hello, you check engine light is designed to come on when there is something malfunctioning with the performance of the engine that effects the vehicles ability to operate efficiently, and increases vehicle emissions.. There are many possible causes, from as simple as the gas cap being too loose (allowing the evaporative emissions system to not be able to function properly to reduce the emissions of fuel vapors), to as complicated as an internal engine problem with one of the cylinders causing engine inefficiency. Being overdue for your oil change will not cause this light to come on. Diagnostic testing is required to find out the root cause of the light coming on. A technician will utilize a diagnostic tool that will retrieve "diagnostic trouble codes" (DTC's) from the engine's processor, which gives the technician clues as to what particular area of engine performance is malfunctioning. This information will lead to specialized testing in the area of concern which will reveal the problem. Good luck!