2003 Ford Mustang Owner Guide 5th Printing - Page 186

Maintenance and Specifications On board diagnostics (OBD-II) Your vehicle is equipped with a computer that monitors the engine's emission control system. This system is commonly known as the On Board Diagnostics System (OBD-II). This OBD-II system protects the environment by ensuring that your vehicle continues to meet government emission standards. The OBD-II system also assists the service technician in properly servicing your vehicle. When the Check Engine/Service Engine Soon light illuminates, the OBD-II system has detected a malfunction. Temporary malfunctions may cause your Check Engine/Service Engine Soon light to illuminate. Examples are: 1. The vehicle has run out of fuel. (The engine may misfire or run poorly.) 2. Poor fuel quality or water in the fuel. 3. The fuel cap may not have been securely tightened. These temporary malfunctions can be corrected by filling the fuel tank with good quality fuel and/or properly tightening the fuel cap. After three driving cycles without these or any other temporary malfunctions present, the Check Engine/Service Engine Soon light should turn off. (A driving cycle consists of a cold engine startup followed by mixed city/highway driving.) No additional vehicle service is required. If the Check Engine/Service Engine Soon light remains on, have your vehicle serviced at the first available opportunity. Readiness for Inspection/Maintenance (I/M) testing In some localities, it may be a legal requirement to pass an I/M test of the on-board diagnostics system. If your "Check Engine/Service Engine Soon" light is on, refer to the description in the Warning lights and chimes section of the Instrument cluster chapter. Your vehicle may not pass the I/M test with the "Check Engine/Service Engine Soon" light on. 186 2003 Mustang (mus) Owners Guide (post-2002-fmt) USA English (fus)