OBDII

OBDII, or On-Board Diagnostics II, is a standardized automotive diagnostic system that monitors emissions-related components and provides self-diagnostic capabilities. It was designed to improve emissions control and simplify diagnosis for technicians and vehicle owners. In the United States, OBD-II became mandatory for all new light-duty vehicles from the 1996 model year and has since been adopted in many regions under variants such as EOBD and JOBD.

OBD-II is accessed via a 16-pin data link connector located under the dash near the driver. It supports several communication protocols, including CAN, ISO 9141-2, ISO 14230-4 (KWP2000), and SAE J1850 PWM or VPW. CAN is the dominant protocol on modern vehicles, providing high-speed data transfer for the diagnostic system and other networks.

The system stores diagnostic trouble codes with five-character codes, starting with P for Powertrain, B for Body, C for Chassis, and U for Network. DTCs may be generic or manufacturer-specific. OBD-II also provides real-time data and diagnostic modes for reading current data, freeze-frame data, clearing codes, and running tests.

Tools ranging from basic readers to advanced scan tools read DTCs and live data, check readiness monitors, and confirm repairs. OBD-II data supports emissions testing and ongoing vehicle maintenance. Limitations include that not all manufacturer-specific data is covered by the base standard, and some data may be restricted. The system’s scope depends on vehicle design and ECU implementation, so older or specialized vehicles may have limited OBD-II functionality.