SAE J1939-73 Diagnostics Application Layer defines the SAE J1939 messages to accomplish diagnostic services and identifies the diagnostic connector to be used for the vehicle service tool interface. Diagnostic messages (DMs) provide the utility needed when the vehicle is being repaired. Diagnostic messages are also used during vehicle operation by the networked electronic control modules to allow them to report diagnostic information and self-compensate as appropriate, based on information received. Diagnostic messages include services such as periodically broadcasting active diagnostic trouble codes, identifying operator diagnostic lamp status, reading or clearing diagnostic trouble codes, reading or writing control module memory, providing a security function, stopping/starting message broadcasts, reporting diagnostic readiness, monitoring engine parametric data, etc. California, EPA, or EU regulated OBD requirements are satisfied with a subset of the specified connector and the defined messages. Aligned parameter and message names throughout this document and harmonized PGN Labels, PGN acronyms, and SPN names with SAE J1939DA and SAE J2403. Added placeholders for new message for Data Value (DM58). Modified DM7 and DM24 as needed for the addition of DM58. Split DM1 into ARB regulated and non-regulated requirements. Clarified message requirements for DM13, DM1, DM2, DM12, DM19, and DM35. Added DM11 actions to include clearing DM2 when OBD regulations require this. Formatted Table 18. Some changes to definitions Updated SPN names in PGN layout to match actual SPN names Strengthened wording around legacy requirements for DM1 (etc) contents with no DTCs to report. Revised other DTC reporting messages to follow the pattern of the recommended settings for unused bytes. Reorganized DM1 for clarity. Revised DM3 and DM11 response requirements. Added OBD compliance codes to stay in synch with SAE J1979.