This SAE Recommended Practice 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 document specifies: a. 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. Behavior of both the vehicle and external test equipment if data is not available, d. A set of diagnostic services, with corresponding content of request and response messages, to satisfy OBD regulations. This document 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 document 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 document is responsible to verify the applicability of each section of this document for a specific vehicle, engine, model year and region. This document is based on the Open Systems Interconnection (OSI) Basic Reference Model in accordance with ISO/IEC 7498 and ISO/IEC 10731 which structures communication systems into seven layers as shown in the table.