OBD

OBD, or on-board diagnostics, is a vehicle’s centralized computer-based system for monitoring the performance of engine and emissions-related components. It provides standardized access to diagnostic trouble codes and real-time data for maintenance, repair, and regulatory inspection. A scan tool connected to the vehicle’s diagnostic port can read DTCs, display sensor data, and clear fault codes when repairs are completed.

The modern OBD standard began as OBD-I in the 1980s with manufacturer-specific implementations. OBD-II was introduced in the United States in 1996 for light-duty vehicles and is now widely mandated and adopted internationally. OBD-II requires a 16-pin on-board diagnostics connector (SAE J1962) and a standardized set of diagnostic trouble codes and data parameters (PIDs). Vehicles use various physical communication protocols, including CAN, ISO 9141-2, ISO 14230 (KWP2000), and SAE J1850; CAN has become dominant since the mid-2000s.

OBD provides both static information (vehicle identification, calibration IDs) and dynamic data (engine rpm, vehicle speed, fuel trim, oxygen sensor readings). DTCs indicate faults and are categorized by system (Powertrain, Body, Chassis, Network). Emissions-related readiness monitors indicate whether a vehicle’s systems have been tested for regulatory compliance; these must complete certain checks before an emissions test passes.

Access to OBD data is widely used by automotive technicians, fleets, and diagnostic software. While enabling, data access and interpretation can vary by jurisdiction, vehicle model, and the level of override or security features in some vehicles.