OBD-II Code Descriptions

OBD-II diagnostic trouble codes (DTCs) are standardized codes generated by a vehicle’s on-board computer system to indicate specific malfunctions. These five-character alphanumeric codes help technicians and diagnosticians identify the system or component at fault and guide troubleshooting. OBD-II codes cover powertrain, body, chassis, and network issues, and reading them with a scan tool is a core diagnostic skill for automotive repair and emissions testin

OBD-II diagnostic trouble codes follow a standardized five-character format that provides immediate insight into the type and location of a fault. The first character identifies the system affected, such as powertrain (P), body (B), chassis (C), or network communications (U). The second character indicates whether the code is generic or manufacturer-specific, while the remaining digits narrow the fault to a specific subsystem or condition. Understanding this structure allows technicians to quickly determine where to begin testing and diagnosis.

OBD-II codes serve as a starting point in the diagnostic process by identifying systems that are operating outside normal parameters. While a code does not automatically identify a failed component, it directs technicians toward the system or circuit requiring further testing. When combined with live data, freeze frame information, and proper diagnostic procedures, OBD-II codes help reduce diagnostic time, prevent unnecessary parts replacement, and ensure accurate repairs—especially for emissions-related faults.