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SAE J1978/ISO 15031-4 specifies a complementary set of functions to be provided by an OBD-II scan tool. These functions provide complete, efficient, and safe access to all regulated OBD (on-board diagnostic) services on any vehicle which is compliant with SAE J1978/ISO 15031-4. The SAE J1978 content of this document is intended to satisfy the requirements of an OBD-II scan tool as required by current U.S. on-board diagnostic (OBD) regulations. The ISO 15031-4 content of this document is intended to satisfy the requirements of OBD requirements in countries other than the U.S., and includes functionality not required or not allowed in the U.S. This document specifies: A means of establishing communications between an OBD-equipped vehicle and an OBD-II scan tool. A set of diagnostic services to be provided by an OBD-II scan tool in order to exercise the services defined in SAE J1979/ISO 15031-5.

On-Board Diagnostic (OBD) regulations require passenger cars, and light and medium duty trucks, to support communication of a minimum set of diagnostic information to off-board “generic” test equipment. This document specifies the diagnostic data which may be required to be supported by motor vehicles and external test equipment for diagnostic purposes which pertain to motor vehicle emission-related data. SAE J1979 was originally developed to meet U.S. OBD requirements for 1996 and later model year vehicles. ISO 15031 5 was based on SAE J1979 and was intended to combine the U.S. requirements with European OBD requirements for 2000 and later model year vehicles.

On-Board Diagnostic (OBD) regulations require passenger cars, and light and medium duty trucks, to support communication of a minimum set of diagnostic information to off-board “generic” test equipment. This document specifies the diagnostic data which may be required to be supported by motor vehicles and external test equipment for diagnostic purposes which pertain to motor vehicle emission-related data. SAE J1979 was originally developed to meet U.S. OBD requirements for 1996 and later model year vehicles. ISO 15031 5 was based on SAE J1979 and was intended to combine the U.S. requirements with European OBD requirements for 2000 and later model year vehicles.

This SAE Recommended Practice supersedes SAE J1978 FEB1998, and is technically equivalent to ISO/DIS 15031-4:December 14, 2001. This document is intended to satisfy the requirements of an OBD scan tool as required by U.S. On-Board Diagnostic (OBD) regulations. The document specifies: a A means of establishing communications between an OBD-equipped vehicle and external test equipment, b A set of diagnostic services to be provided by the external test equipment in order to exercise the services defined in SAE J1979, c Conformance criteria for the external test equipment.

SAE J1978 defines the requirements of the OBD II scan tool. SAE J2201 defines the minimum requirements of the vehicle communications interface for the SAE J1978 OBD II scan tool. This interface connects the SAE J1962 test equipment connector to the hardware/software of the SAE J1978 OBD II scan tool that will use this interface to communicate with vehicles for the purpose of accessing required OBD II functions. Included in this SAE Recommended Practice are several definitions relating to the interface, and interface functionality evaluation. Appendix A - Examples include several example interface circuit implementations, which are believed to meet the requirements of this document and of SAE J1978. These examples are NOT requirements of this document. They are provided to assist circuit designers in developing interface circuits. Appendix B - Supporting Documents includes a list of supporting documents for the examples shown in Appendix A.