After you have studied and completely understand the system and its capabilities you can then begin your diagnosis using basic and logical methods. I cannot over emphasize the importance of logical troubleshooting. The ability to diagnose a problem that will lead you to the cause of the malfunction and its eventual solution is what separates an automotive technician from a parts changer.
Using logical diagnosis
In short this means following the most simple and basic procedures. Starting with the most likely cause and working towards the most unlikely cause. In other words check out the easiest most obvious solutions first before proceeding to the less likely ones.
The more you jump around from place to place the less likely you are to uncover the problem in a timely manner unless you are extremely lucky which I am not. Try not to guess at the problem or jump to conclusions before considering all the factors involved.
Often it is the logical approach that will solve even the most complicated electrical and electronic engine control problems. You also want to remember to check all of the traditional nonelectric engine control possibilities before attempting to diagnose the more complicated electrical side of the engine control systems itself.
Isolating problem areas
The logical troubleshooting procedure would then be to check the input sensors and wiring first, and then the output devices and their wiring, and finally the computer last. Most late model computerized engine controls have self-diagnostic capabilities built-in. A malfunction in any sensor or output device including the computer itself should (not always) store a trouble code in the computer's memory.
Things like a bad coil pack a failed sparkplug or defective ignition wires are not only the easiest things to check first but also would be the most common problems that would set this code. The power of logical diagnosis can solve many automotive problems.
If you are thinking about purchasing some tools to get the job done I have a recent review of the new release Actron auto scanner. This next link will take you back to the auto repair blog from this page about diagnosing electrical engine control systems.