How?
As far as I remember, here in the United States, the federal government mandated a standardized vehicle port connection and standardized software so the general public could diagnose their own cars and keep the manufacturers/dealers from holding a repair monopoly. That standard is now called OBDII. That "standard" has had many changes over the years (always backwards compatible) and does NOT keep manufacturers from improving their products. Vehicle emissions really don't have anything do specifically with OBDII. Emission standards were around long before OBDII, before OBDI, and even before cars ever had computers.
