What is a Diagnostic Trouble Code (DTC) and how is it structured?

DTCs are standardized codes identifying detected faults. The five-character format includes: First letter (P=Powertrain, B=Body, C=Chassis, U=Network), Second digit (0=SAE standard, 1=manufacturer-specific), Third digit (system area), and last two digits (specific fault). For example, P0301 indicates cylinder 1 misfire. When a fault is detected, the ECU sets the DTC, illuminates the warning light, and often stores freeze frame data. Technicians use scan tools to read DTCs for diagnosis.