The purpose of this Recommended Practice is to verify that vehicles and/or components are capable of communicating a required set of information, in accordance with the diagnostic messages specified in SAE J1939-73, to fulfill the off-board diagnostic tool interface requirements contained in the government regulations cited below. This document describes the tests, methods, and results for verifying diagnostic communications from an off board diagnostic tool (i.e., scan tool) to a vehicle and/or component. SAE members have generated this document to serve as a guide for testing vehicles for compliance with ARB and other requirements for emissions-related on-board diagnostic (OBD) functions for heavy duty engines used in medium and heavy duty vehicles. The development of HD OBD regulations by US EPA and California's Air Resources Board (ARB) require that diagnostic message services are exercised to evaluate diagnostic communication standardization requirements on production vehicles. The user should reference the summary provided by SAE J1939-73 Table 1 and Table 2 for OBD compliance support. The December 2008 publication of J1939-84 described a test process for EURO IV and EURO V engine emissions and diagnostics regulations, which is given in section 7. The December 2010 version of the document added a test plan and procedures for ARB and US EPA HD OBD requirements with emphasis on 13 CCR 1971.1 (l)(1) Verification of Standardized Requirements, as section 6. The June 2012 version added the observation of the MIL On to MIL Off transition for a single trip CCM fault and reformatted tables in section 6 to improve ease of use.