Technical 22 Inspect evidence: Turning information into diagnostic direction In the latest article in our series from Darren Quinn of Mechanic Mindset, we explore the second stage in the ‘FIXDIT’ diagnostic framework: ‘Inspect evidence’. Other articles in the series can be found on the Aftermarket Magazine website at tinyurl.com/AM-FIXDIT as they are published. S uccessful diagnostics has never been about luck. The best technicians follow a process. Whether diagnosing an intermittent electrical fault, a drivability issue or a complex network communication problem, the same fundamental stages must be followed. The challenge is that many technicians don’t consistently apply them. Steps are skipped, assumptions are made, and testing begins before the problem is fully understood. The FIXDIT framework was created by Mechanic Mindset to provide a simple, memorable way of applying these essential diagnostic stages every time. It stands for Find evidence, Inspect evidence, eXecute diagnostic plan, Determine the cause, Implement repair and Test. In the previous article, we focused on Finding evidence: gathering information from the customer, carrying out a full function test, inspecting the vehicle, and preserving every piece of available evidence. This month we move on to the second stage: Inspect Evidence. Think before you test Modern workshops are full of sophisticated diagnostic equipment. Scan tools, oscilloscopes, multimeters and pressure transducers have transformed the way we diagnose vehicles. However, none of these tools decides what should be tested next. That responsibility belongs entirely to the technician. One of the biggest mistakes in diagnostics is moving too quickly from gathering evidence to testing components. It is tempting to begin checking voltages, disconnecting connectors or measuring signals immediately, but testing without direction often creates more questions than answers. Professional diagnosticians pause before they test. They step back from the vehicle and ask a simple question: “What is the evidence actually telling me?” The answer to that question shapes everything that follows. Build a theory The purpose of the ‘Inspect evidence’ stage is not to identify the fault. It is to develop the most likely theory based on the evidence collected. Think of the previous stage as gathering the pieces of a jigsaw puzzle. ‘Inspect evidence’ is where those pieces begin to fit together. Your theory should explain every symptom you’ve observed. If it doesn’t, either your theory is incomplete or more evidence is needed. This is a subtle but important shift in thinking. The next stage of FIXDIT is about proving or disproving the theory you’ve developed here. Every fault has a story One of the most valuable questions a technician can ask is: “What changed?” Vehicles rarely develop faults without a reason. Something has changed within the vehicle’s history, environment or operating conditions. Perhaps the fault appeared after another repair. Maybe it started following accident damage, a windscreen replacement or prolonged exposure to heavy rain. These changes often provide the missing link between the customer’s complaint and the underlying cause. Imagine a vehicle suffering intermittent CAN communication faults. Initial instinct might be to start measuring network voltages and checking termination resistors. However, if the evidence shows the problem began immediately after a replacement windscreen was fitted, the investigation suddenly has direction. Attention shifts towards disturbed wiring, trapped harnesses or water ingress around the A-pillars. The evidence has created a logical theory. Look for common denominators Another habit that experienced diagnosticians will have formed is looking for what the symptoms have in common. When several faults appear together, resist treating them as separate problems. Ask yourself: “What do these faults have in common?” A vehicle may present with inoperative
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