The OBD2 standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each. There is a pin in the connector that provides power for the scan tool/OBD Digital Chip Tuning Box from the vehicle battery, which eliminates the need to connect a scan tool/tuning box to a power source separately. Finally, the OBD2 standard provides an extensible list of DTCs. As a result of this standardization, a single device can query the on-board computer(s) in any vehicle.
OBD2 standardization was prompted by emissions requirements, and though only emission-related codes and data are required to be transmitted through it, most manufacturers have made the OBD2 Data Link Connector the only one in the vehicle through which all systems are diagnosed and programmed. OBD-II Diagnostic Trouble Codes are 4-digit, preceded by a letter: P for engine and transmission (powertrain), B for body, C for chassis, and U for network. The OBD2 connector is required to be within 2 feet (0.61 m) of the steering wheel (unless an exemption is applied for by the manufacturer, in which case it is still somewhere within reach of the driver).
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