Technical 24 November 2026 ǁǁǁ͘ ĂŌĞƌŵĂƌŬĞƚŽŶůŝŶĞ͘ ŶĞƚ Determine the cause: Fix the reason, not just the result In the latest article in our series from Darren Quinn of Mechanic Mindset, we explore the fourth stage in the ‘FIXDIT’ diagnostic framework: ‘Determine the cause’. Other articles in the series can be found on the Aftermarket Magazine website at tinyurl.com/AM-FIXDIT as they are published. Successful diagnostics depends on following a structured process. The FIXDIT framework provides a simple way to remember six essential stages: Find Evidence, Inspect Evidence, eXecute Diagnostic Plan, Determine the Cause, Implement Repair and Test. In previous articles, we’ve gathered evidence, analysed it to develop a theory, and carried out structured testing to identify the fault. Now we reach the fourth stage: Determine the cause. Finding a failed component is an important achievement, but it doesn’t necessarily mean we’ve finished diagnosing the problem. There is still one critical question to answer: “Why did it fail?” Finding the fault isn’t finding the cause Imagine diagnosing a vehicle with an inoperative cooling fan. After following a logical test plan, you identify a blown fuse. Replacing it restores operation, and everything appears to be working correctly. Job complete? Not necessarily. The fuse failed for a reason. Perhaps the fan motor is drawing excessive current, the wiring has been damaged, or an intermittent short circuit exists somewhere in the system. Replacing the fuse has corrected the symptom, but the underlying problem may still be present. This distinction is fundamental to professional diagnostics. A failed component is sometimes the cause of the customer’s complaint, but it may also be the consequence of another problem. Understanding the difference is what prevents repeat failures and unnecessary comebacks. The power of asking why One useful technique for investigating root causes is the ‘five whys’ method. The principle is simple: repeatedly ask why something happened until you reach the underlying cause. Consider a vehicle with inoperative rear lighting. Why are the rear lights not working? Because the circuit has an excessive voltage drop. Why is there excessive voltage drop? Because corrosion has developed inside a connector. Why has the connector corroded? Because water has entered the electrical connection. Why is water entering the connection? Because the rear light housing isn’t sealing correctly. Why isn’t it sealing correctly? Because the seal was damaged during a previous repair. Without investigating further, the technician might simply clean the connector and restore operation. However, unless the damaged seal is
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