OBD (On Board Diagnostics) port II, I is a federally mandated feature for all automobiles sold in United States after they year 1985. The port was originally intended to provide a standardized interface for the diagnosis of emission-related malfunctions. There are currently three communications standard for OBD-II compliant vehicles : ISO-9141-2, SAEJ1978 VPW, and SAEJ1978 PWM.

The standards vary in the method by which is transmitted from the car to the receiver.