A vehicle diagnostic system comprising: an electronic control unit on-board a vehicle configured to monitor at least one vehicle system for one or more fault conditions and to generate one or more corresponding fault codes; a vehicle bus plug connector on-board the vehicle, the vehicle bus plug connector being non-compatible with OBD protocol; a vehicle bus extending between and coupling the vehicle bus plug connector with the electronic control unit to enable the communication of electrical signals between the electronic control unit and the vehicle bus plug connector; and a removable diagnostic connector module including a diagnostic service connector forming an on-board diagnostic port of the vehicle for establishing connection with an external diagnostic scan tool via OBD protocol, an electronic communication module electrically coupled with the diagnostic service connector, a housing enclosing the electronic communication module, and an integrated vehicle bus connector having a plurality of terminals electrically connected to the electronic communication module, the plurality of terminals being configured for making a plug-type connection with the vehicle bus plug connector, wherein the electronic communication module of the diagnostic connector module is configured to transfer the one or more fault codes from the electronic control unit to an external diagnostic scan tool via the diagnostic service connector of the diagnostic connector module, and wherein the electronic control unit on-board the vehicle is only operable to communicate with the external diagnostic scan tool when the diagnostic connector module is coupled to the vehicle bus plug connector. an electronic control unit on-board a vehicle configured to monitor at least one vehicle system for one or more fault conditions and to generate one or more corresponding fault codes; a vehicle bus plug connector on-board the vehicle, the vehicle bus plug connector being non-compatible with OBD protocol; a vehicle bus extending between and coupling the vehicle bus plug connector with the electronic control unit to enable the communication of electrical signals between the electronic control unit and the vehicle bus plug connector; and a removable diagnostic connector module including a diagnostic service connector forming an on-board diagnostic port of the vehicle for establishing connection with an external diagnostic scan tool via OBD protocol, an electronic communication module electrically coupled with the diagnostic service connector, a housing enclosing the electronic communication module, and an integrated vehicle bus connector having a plurality of terminals electrically connected to the electronic communication module, the plurality of terminals being configured for making a plug-type connection with the vehicle bus plug connector, a diagnostic service connector forming an on-board diagnostic port of the vehicle for establishing connection with an external diagnostic scan tool via OBD protocol, an electronic communication module electrically coupled with the diagnostic service connector, a housing enclosing the electronic communication module, and an integrated vehicle bus connector having a plurality of terminals electrically connected to the electronic communication module, the plurality of terminals being configured for making a plug-type connection with the vehicle bus plug connector, wherein the electronic communication module of the diagnostic connector module is configured to transfer the one or more fault codes from the electronic control unit to an external diagnostic scan tool via the diagnostic service connector of the diagnostic connector module, and wherein the electronic control unit on-board the vehicle is only operable to communicate with the external diagnostic scan tool when the diagnostic connector module is coupled to the vehicle bus plug connector.