If you're familiar with the concept of computer controllers for auto engines, FADEC is the same basic idea with a jet engine. A group of sensors feeding the computer, and the computer calculating the appropriate fuel (and other parameters it can adjust) to get optimum fuel burn and emissions from the engine. Like the car computer, it can report problems in the form of codes, but the "codes" are reported "live" to the EICAS system in the airplane. Unlike the auto, the throttle is electronic instead of mechanical. FADEC also has the benefit of protecting the engine from overstress in that it prevents the pilot (or other circumstances) from causing excessive EGT, excessive N1 or N2 speeds etc. that can damage or shorten the service life of the engine.
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Safe flying to you...
[This message has been edited by Flight Safety (edited 20 January 2001).]