1998 Ford Expedition Owner Guide 1st Printing - Page 7

Instrumentation the engine is started, one of the engine's emission control systems may be malfunctioning. The light may illuminate without a driveability concern being noted. The vehicle will usually be drivable and will not require towing. What you should do if the check engine light illuminates Light turns on solid: This means that the OBD II system has detected a malfunction. Temporary malfunctions may cause your Check Engine 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 properly installed and securely tightened. These temporary malfunctions can be corrected by filling the fuel tank with good quality fuel and/or properly installing and securely tightening the gas cap. After three driving cycles without these or any other temporary malfunctions present, the Check Engine 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. 7