This part of ISO 15031 is intended to satisfy the data reporting requirements of On-Board Diagnostic (OBD) regulations in the United States and Europe and any other region that may adopt similar requirements in the future. This part of ISO 15031 specifiesa) message formats for request and response messages,b) timing requirements between request messages from external test equipment and response messages from vehicles and between those messages and subsequent request messages,c) behaviour of both the vehicle and external test equipment if data are not available, andd) a set of diagnostic services, with corresponding content of request and response messages, to satisfy OBD regulations.This part of ISO 15031 includes capabilities required to satisfy OBD requirements for multiple regions, model years, engine types, and vehicle types. Those regulations are not yet final for some regions and are expected to change in the future. This part of ISO 15031 makes no attempt to interpret the regulations and does not include applicability of the included diagnostic services and data parameters for various vehicle applications. The user of this part of ISO 15031 is responsible for verifying the applicability of each clause of this part of ISO 15031 for a specific vehicle, engine, model year, and region.This part of ISO 15031 specifies diagnostic services and functionally addressed request/response messages required to be supported by motor vehicles and external test equipment for diagnostic purposes which pertain to motor vehicle emission-related data. Any external test equipment meeting the requirements of ISO 15031-4 use these messages to retrieve emissions-related information from the vehicle.Each clause in this part of ISO 15031 which specifies additional details to existing clauses of ISO 9141-2, ISO 14230-4, SAE J1850, and ISO 15765-4 supersede those specifications.