Common obd connectors have only one line connected to the plugs on both sides to provide power or data transmission for the vehicle OBD.

​Before OBD-I, each manufacturer had their own set of standards for OBD, meaning that mechanics had to buy expensive scan tools for each manufacturer.

Diagnostic Trouble Codes (DTC) are stored in the computer system. Codes can vary from one manufacturer to another. However, anyone with an OBD-II scan tool can connect to the port and read the diagnostic trouble codes from the computer.

Traditionally, a mechanic would hook up a scan tool to the port to read the DTC. Less expensive scanners would only provide a numeric code, which the mechanic would then look up from the manufacturer’s manual or service website.