OBD1 and OBD2 are similar in many ways, but there are also some important differences. OBD1 systems are more basic and less comprehensive than OBD2 systems. OBD1 systems typically only monitor emission control systems, while OBD2 systems monitor a wide range of engine and emission control systems, as well as other systems such as the transmission, ABS, and airbags.

Another difference between OBD1 and OBD2 is the way that they communicate. OBD1 systems use a variety of different communication protocols, while OBD2 systems use a standardized protocol called CAN (Controller Area Network). This makes it easier to diagnose problems with OBD2 vehicles, as all OBD2 scanners use the same protocol.