What is onboard diagnostics?

On-board diagnostics (OBD) is the vehicle's terminology, which points to the vehicle's ability to diagnose and report itself. OBD systems give vehicle owners or service technicians access to the individual vehicle subsystems. The number of information supplied via OBD diagnostics varies greatly from the version of the car-mounted computer in the early 1980s. Earlier versions of OBD only illuminate fault lights or "idiot lights" if a problem is detected, but will not provide any information to explain the nature of the problem. Modern OBD implementations use a standardized digital communication port in addition to the standardized series of diagnostic fault codes, or fault codes, which allow a fast identification and remediation of automotive faults to provide real-time data.

OBD-II Diagnostic Connector

The 15031-3 specification provides two standardized hardware interfaces, known as type A and type B, both female, 16-pin (2x8), D-connector, and have a notch between the two rows of the pin. But the type B is interrupted in the middle, so you can't plug the type a male connector into a type B receptacle. You can, however, mate a Type B plug in a female socket.

The type a connector is used for vehicles with 12V supply voltages, while Type B is used for 24V vehicles and it needs to be marked in front of the blue D-shaped area.

Reprinted from Auto diagnosis Scanner

What is onboard diagnostics?