23/06/2026
What is diagnostics? How long will it take?
Questions we hear surprisingly often, usually from owners who imagine the process begins and ends with plugging a computer into the vehicle and reading what it has to say.
In reality, diagnostic equipment is just one source of information. Modern vehicles generate an enormous amount of data, but data on its own rarely explains the root cause of a fault. The real value lies in understanding what that information means and how it relates to the symptoms being experienced.
A technician will typically begin by gathering information, reviewing fault codes, examining live data and understanding how the system is intended to operate. From there, a theory starts to emerge. If that theory is correct, certain evidence should exist somewhere within the vehicle, whether that’s a failed component, a wiring issue, an unexpected signal or a mechanical defect.
The investigation then becomes a process of testing that theory.
The damaged splice joint shown here is a good example. Hidden within the wiring harness, it was impossible to see during normal use and gave no obvious indication of its condition. The fault symptoms suggested a particular area of concern, and further testing led us to the section of wiring where the defect was eventually found.
Once exposed, the problem appears relatively straightforward. Looking back from the answer, it’s easy to convince yourself that the fault was obvious all along.
Diagnostics rarely works that way.
The real skill lies in taking a collection of symptoms, observations and test results, and using them to predict where the fault is likely to be before it’s ever seen.
That’s proper diagnostics ❤️
