An OBDII protocol is part of an on-board self-diagnostic system in your vehicle that allows you or your mechanic to access information about it and it's systems. OBD or onboard diagnostics was first created by VW for internal use however, the system quickly spread out and it first became standardised in 1996. Different regions and countries made it mandatory for new vehicles at different times and Australia did so in 2006 for petrol vehicles and 2007 for diesel cars. Today OBDII is the only protocol to get information from your car about issues or generally about how it works. More modern vehicles require you to connect to its OBDII port before you do anything on them.