PRIMARY INSPECTION
If the problem area is visible, look it over to check for damage due to corrosion, stretched or cut wire harnesses, fluid leaks, physical cracks and worn out parts. Depending on the concern you are diagnosing rather it is mechanical or electrical related using you senses can be a valuable asset in the diagnostics process. For instance pulsating brake peddle front end shutter and steering wheel vibration point to a front end suspension area as a starting point. Central vents are blowing out cold air and the defrost mode output is warm air just to name a few simple examples.
DIAGNOSTIC TESTS
Depending on if you have it available through a service information provider rather it is OEM or aftermarket. Check for technical service bulletins ,recalls software updates that apply to the concern. Also make sure to look at description and operation for systems. This can not be stressed enough especially when dealing with electrical based concerns that could be communication faults/ performance issues etc. I have seen customer concerns that were nothing more than a misunderstanding in a system and its functions/features.
If you do not have a clear understanding of a system and its design purpose. How can you be diagnose it to find the source of a fault? Looking up the correct schematic is critical here too; OEM schematics should take precedence over aftermarket ones and at least have both available to do a comparison and get the best information possible if one schematic lacks information that the other possesses. A good schematic in a diagnostic strategy sets you up to know what your expected values should be doing testing. Which point you to any faults in a system if those expected values are not obtain during testing.
DATA ANALYSIS
After performing any diagnostic tests, record your findings and keep it organized! This trait alone separates the season vets form the rookie automotive technicians. Keeping good notes during a diagnostics process can make or break you getting paid. This is especially true if you work for an OEM manufacturer. Along with making it easier for customers to see how thorough you are this creates a level of trust. When you are transparent in how you came to the solution to their concern. At this point you are taking you gathered information and comparing it to OEM specifications. Plus relevant known good data and your experience/training on how a particular circuit should operate. According to established standards of continuity, voltage drop, ohms law etc.
RECOMMENDATION OF SERVICES
Now based on your results from prior data and research gathering and verifying the faults if present found. You should be able to recommend the correct course of action now. Leading you to getting the vehicle back on the road. If all these stages are perform correctly. Selling diagnostic service to a customer and explaining to them how you came to your decision for recommended services should be a breeze.
EXTRA CREDIT
Never assume based on the customer’s concern you know what the problem is, relying on past experience without proper testing . Simply put this is guessing (an educated guess at best) and if diagnostic testing is perform relying on a previous diagnose vehicles you can leave yourself susceptible to tunnel vision. Steering blindly while ignoring the more important symptoms and data that could lead to proper solution. Diagnose never Guess!