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 test 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, test methods, and results for verifying diagnostics ommunication 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 December 2008 publication of J1939-84 described a test process for EURO IV and EURO V engine emissions and diagnostics regulations. 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 (I)(1) Verification of Standardized Requirements. The user should reference the summary provided by SAE J 1939-73 Table 1 and Table 2 for OBD compliance support.