With a basic understanding of these principals and a little practice you will soon be able to navigate these complex systems. When diagnosing the modern vehicle just remember to follow the data. The data that you gather during your diagnoses will always guide you to the problem.
When a vehicle has been in failsafe or limp mode, it is important to check for codes to see what has caused this condition. If multiple codes are present, check to see whether there is something in common with each one.