ISO 15031-4:2014 specifies a set of standard diagnostic services to be provided by vehicles (OBD services). ISO 15031-4:2014 specifies a complementary set of facilities, to be provided by external test equipment, which will include scan tool facilities. These facilities provide complete, efficient, and safe access to all of the public OBD (on-board diagnosis) services on any vehicle, which is compliant with ISO 15031-4:2014.

ISO 15031-4:2014 specifies

- a means of establishing communications between an OBD-equipped vehicle and external test equipment, and

- a set of diagnostic services to be provided by the external test equipment in order to exercise the services defined in ISO 15031‑5.

ISO 15031-4:2014 does not preclude the inclusion of additional capabilities or functions in external test equipment. However, it is the responsibility of the external test equipment designer to ensure that no such capability or function can adversely affect either an OBD-equipped vehicle, which may be connected to the external test equipment or the external test equipment itself.