SuperG,
Ah, Gary there have been whole books written to answer that question. That having been said, I'll try to give you the Readers Digest version.
The engine is controlled by a micro-processor, a computer, or as Ford referres to it an Electronic Engine Controller.
It controls the DIS (Distributorless Ignition System),and the EFI (electronic Fuel injection). Internal combustion engine basics, you have to have fuel and spark.
The computer is programmed to respond to the information it receives from a number of sensors, for example the TPS (Throttle Position Sensor), which tells the computer the degree of "open" the throttle plate is at. The wider the throttle plate is open, the computer tells the injectors to stay open longer to add fuel.
As to how you can test the "SYSTEM". It has a system for self testing. If the computer gets a signal from a sensor that is "out of the expected range" it records a "code". To check the system you "pull the codes".
Keep in mind that the sensors can only communicate with the computer in electrical terms, i.e. volts, ohms, amps and/or fractions thereof. So a code could mean a sensor has failed, or it could indicate a connection or wire is at fault.
A sensor code could mean that the sensor is sending bad information because of a fault elsewhere, e.g. an oxygen sensor is not switching and staying on the lean side due to a vacuum leak.
This is very brief and very basic, but it is the start of your learning process if you want to learn. Do a search on how to access the codes, and the lists of the code numbers, and their meaning. Then try accessing YOUR codes, if any!
Anybody else want to jump in here? thumb rangerj
