DTC

📖 YOUCANIC Automotive Glossary

A DTC (Diagnostic Trouble Code) is a standardized five-character alphanumeric code that a vehicle’s electronic control module stores in memory when its onboard diagnostic system detects a malfunction. Each code follows the SAE J2012 standard: the first character indicates the system (P for Powertrain, B for Body, C for Chassis, U for Network), the second character indicates whether the code is generic (0) or manufacturer-specific (1), and the remaining three characters identify the specific subsystem and fault. For example, P0301 means Powertrain, generic, ignition system, cylinder 1 misfire. DTCs are read using an OBD2 scanner connected to the vehicle’s DLC.

DTCs exist in several states: active/current (fault happening now), pending (detected once, needs second confirmation), history/stored (occurred previously but not currently present), and permanent (cannot be cleared by scan tool, only self-clears after ECU verifies repair on 2010+ vehicles). Understanding DTC states helps DIYers prioritize repairs. Always read freeze frame data associated with each DTC before clearing codes — this snapshot of engine conditions at the time of the fault provides critical diagnostic context that is permanently lost once codes are erased.