1996 Ford F250 Owner's Manual - Page 72

NOTE: If your light truck is equipped with dual fuel tanks, the "CHECK ENGINE" light may come on if fuel is restricted to the engine or if the fuel flow is momentarily disrupted because of an empty fuel tank before you switched to the auxiliary fuel tank. This condition is normal and the light should go off after full fuel flow is restored. An example of a condition which corrects itself occurs when an engine running out of fuel begins to misfire. In this case, the Check Engine Warning Light may turn on and will then set a Diagnostic Trouble Code indicating that the engine was misfiring while the last of the fuel was being consumed. After refueling, the Check Engine Warning Light will turn off after the vehicle has completed three consecutive warm up cycles without a misfire condition occurring. A warm up cycle consists of engine start from a cold condition (engine at ambient temperature) and running until the engine reaches normal operating temperature. On the fourth engine start up, the Check Engine Warning Light will turn off as soon as the engine begins to crank. It is not necessary to have the engine serviced. Under certain conditions, the Check Engine Warning Light may come on if the fuel cap is not properly installed. If the Check Engine Warning Light comes on and you suspect that the fuel cap is not properly installed, pull off the road as soon as it is safely possible and turn off the engine. Remove and replace the fuel cap, making sure it is properly seated. 70