Your car or trucks check engine light, which is located on the instrument panel, is there to alert you concerning your vehicle's onboard diagnostics (OBD) system. Engine Control Modules (ECM) control and monitor vehicle’s engine and transmission performance and is continually adjusting & monitoring many variables such as: as engine speed (RPM), fuel mixture, and ignition timing, and optimizing automatic transmission shift timing. When the electronic-control system finds a problem it cannot adjust, the ECM stores a code and lights the yellow warning indicator. These diagnostic trouble codes, also known as “P” codes help a properly trained auto diagnostic technician determine the probable source of the problem. Each vehicle manufacturer uses a specific software that is unique. It is necessary to have the proper diagnostic equipment which can communicate with the OBD system. Where and how the ECM computer is accessed varies and depends on the make, model and year of the vehicle.