For automotive technicians, scan tools are indispensable for diagnosing vehicle issues. We rely on them to quickly access Diagnostic Trouble Codes (DTCs) and streamline the repair process. The understanding has generally been that standardized processes ensure DTCs, like P0*** codes, are universally consistent across different scan tools. However, experience sometimes throws a curveball, challenging these assumptions.
Like many seasoned mechanics, I’ve used a range of scan tools over the years. My older Actron scan tool, a common sight in shops for the past two decades, has been reliable for quick code pulls, generic data checks, and readiness monitor assessments. For more intricate diagnostics and complex jobs, my go-to tool is the Snap-On Solus Edge, equipped with the latest software. The expectation is that these tools, especially a professional-grade one like the Snap-On, should provide clear and consistent diagnostic information.
Recently, I encountered a situation that highlighted a surprising discrepancy between these tools. During a diagnostic session, both the Actron and the Snap-On Solus Edge indicated only one DTC was present. However, they disagreed on the specific code. The Snap-On reported a P0300 (Random/Multiple Cylinder Misfire Detected), while the Actron displayed a P0305 (Cylinder 5 Misfire Detected).
Initially, my inclination was to trust the Snap-On tool as potentially more accurate and comprehensive. Yet, past experiences have taught me that even advanced tools can sometimes be misleading. The key to resolving this diagnostic puzzle lay in delving deeper into the data provided, specifically the engine misfire data available through the Snap-On scan tool.
Examining the engine misfire data on the Snap-On revealed crucial insights. It indicated active misfire counts on both cylinders 4 and 5, registering as dead misses on both. This data aligned perfectly with the vehicle’s symptoms – frequent engine stalling, a condition not typically associated with a single cylinder misfire. This pointed towards a more widespread issue affecting multiple cylinders, corroborating the P0300 code from the Snap-On but also partially aligning with the cylinder 5 focus of the Actron.
Further investigation with an ignition scope confirmed the misfire issue and pinpointed the location. Cylinders 4 and 5 showed spark firing outside the cylinder, characterized by low KV readings and normal burn lines – almost mimicking a waste spark event. Interestingly, cylinders 4 and 5 are on different engine banks but are sequentially positioned in the firing order.
The root cause was ultimately traced to a faulty distributor cap. Replacing the cap resolved the misfires, although a subsequent check revealed an occasional high KV event on the #4 plug wire, suggesting a potential secondary issue. In retrospect, both scan tools provided pieces of the diagnostic puzzle. The Actron was more specific, pointing to cylinder 5, while the Snap-On, with its P0300 code and, crucially, the engine misfire data, painted a broader and more accurate picture of a multi-cylinder problem. While the Actron wasn’t entirely wrong, it missed the full scope of the misfire issue impacting both cylinders 4 and 5.
In hindsight, it would have been insightful to test the Actron further by selecting vehicle models one year older or newer. This might have revealed if the code interpretation varied across different model year selections on the older tool.
This experience underscores a vital lesson for automotive diagnostics: while DTCs provide a starting point, relying solely on a single code from a single tool can be limiting. Leveraging the detailed data offered by advanced scan tools like the Snap-On, particularly engine misfire data, is crucial for a comprehensive and accurate diagnosis. Have other technicians encountered similar discrepancies in generic DTC readings across different scan tools? Sharing these experiences can further refine our diagnostic approaches and highlight the importance of utilizing in-depth data analysis for effective automotive repairs.
