DTC — gnostic Trouble Code

A DTC is the 5-character alphanumeric code stored by the ECU when a fault or out-of-range condition is detected. Format per SAE J2012: first letter is the system (P=Powertrain, C=Chassis, B=Body, U=Network), followed by 4 hexadecimal digits.

DTCs are how the ECU communicates "something is wrong" to the diagnostic scan tool. Whether a code is genuine (real fault) or nuisance (false positive) determines whether you fix the underlying cause or apply DTC OFF at the ECU level. Always diagnose before suppressing.