One problem related to service engine light on has been reported for the 1999 Ford E-350. The most recently reported issues are listed below.
Had an engine failure while towing a boat. Had brakes but no power brakes. This happened on July 30, 2005. The service engine light came on and a few second later the engine failed. The module that controlled the fuel injection failed. There was a hole coin the back of it, and it affected the whole engine. Water dripped out of the part when the mechanic took it off.