ISO 27145-3:2012 defines the implementation of a subset of unified diagnostic services (UDS) specified in ISO 14229-1. The diagnostic services are used to communicate the diagnostic data defined in ISO 27145-2.

The subset of unified diagnostic services derives from the requirements stated in the World-Wide Harmonized On-Board Diagnostic Global Technical Regulations (WWH-OBD GTR). The common message set defined in ISO 27145-3:2012 is independent of the underlying transport, network, data link and physical layer. ISO 27145-3:2012 does not specify any requirements for the in-vehicle network architecture.

ISO 27145-3:2012 is compatible with ISO 14229-1 and includes provisions to support the data set of SAE J1979-DA and SAE J2012-DA WWH-OBD.

ISO 27145-3:2012 is intended for use with ISO 27145-4, which is the entry point for the protocol initialization and is based on two different data links:

• Diagnostic communication over Controller Area Network (DoCAN), ISO 15765-1, ISO 15765-2, ISO 15765-4;
• Diagnostic communication over Internet Protocol (DoIP), ISO 13400 (all parts).

ISO 27145-3:2012 includes capabilities required to satisfy OBD regulations for multiple regions, vehicle types, model years, and engine types. Those regulations are not yet final for some regions and are expected to change in the future. ISO 27145-3:2012 does not attempt to interpret the regulations and does not include applicability of the included diagnostic services and data parameters for various vehicle applications. It is intended that users of ISO 27145-3:2012 verify the applicability of each of its clauses for a specific vehicle, engine, model year and region.