DTC
Diagnostic Trouble Code — fault code from the ECU.
A DTC is a five-character code that the ECU stores when it detects a deviation. The first character identifies the system (P = powertrain, B = body, C = chassis, U = network), and the next four digits pinpoint the fault. Example: P0420 = "Catalyst efficiency bank 1 below threshold". DTCs are categorized as stored (Mode 03), pending (Mode 07) and permanent (Mode 0A).