As much as vehicle diagnosis is dynamic and involves more than one tool and can take different form in regards to an issue at hand, it is important to lay down a procedural process to ensure the task at hand is executed skillfully
Verify that indeed the problem/fault a client has raised on his vehicle indeed exists and confirm the symptoms.
2. Collect Information
Get more information in regards to the problem at hand, can the driver give more info? is there a correlation between the problem and an action the driver has noted? Example; car jerks only when reverse gear is engaged
Stop and think logically, consider what you now know. Does the information you have help you to narrow down to one area of examination?
Measure and compare. Use your diagnostic equipment that can assist to measure data or gather information in regards to the problematic area. Carry out tests that will assist you to pin point the actual problematic area or part.
Having establish the problem rectify or replace the part if it's faulty. If for instance the over heating of a vehicle was caused by a stuck thermostat, replace, top up coolant to the recommended level etc.
Make sure the system is now working well. Post test the same problematic area or issue. Also check that your applied solution has not caused a further problem. Run a post repair/replacement system scan or inspection. Eg replacement of a thermostat could result in a new problem of coolant leaking if the thermostat housing isn't fixed appropriately. Run tests after repair or replacement