Posted on 12/19/2025
Most drivers think of a “diagnostic” as plugging in a scanner to read a check engine light code. In reality, a proper diagnostic session can reveal far more than a single trouble code. Modern vehicles constantly record data about how sensors, modules, and mechanical parts are behaving, even when no light is on. When a technician knows how to read that information, it can uncover problems long before you are stuck on the side of the road. 1. Old or Hidden Faults That Never Turn On the Light Your car’s computers store information even when the dash looks perfectly normal. Some faults only show up for a moment, then disappear before the light has time to come on. Others are stored as “history” or “pending” codes that never turn into an obvious warning. During a diagnostic, technicians can see: Past misfires that happened under certain load or rpm Short-term voltage drops that hint at battery or wiring issues Intermittent sen ... read more