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.
SAE J1978/ISO 15031-4 does not preclude the inclusion of additional capabilities or functions in an OBD-II scan tool. However, it is the responsibility of the OBD-II scan tool designer to ensure that no such capability or function can adversely affect either an OBD-equipped vehicle, which may be connected to the OBD-II scan tool, or to the OBD-II scan tool itself.
Differences in the SAE J1978 and ISO 15031-4 requirements are highlighted by bold italic text in the technical requirements sections of this document. Notable examples are:
Current U.S. OBD regulations will permit ISO 15765-4 as an allowable OBD serial data link at 500 kbps only. Only those provisions of ISO 15765-4 that pertain to 500 kbps are required to be supported by an SAE J1978 diagnostic scan tool.
Current U.S. OBD regulations will not allow greater than 20 V at the SAE J1962 connector. Only the Type A connector as defined in SAE J1962/ISO 15031-3 needs to be supported by an SAE J1978 diagnostic scan tool.
Rationale
This SAE Recommended Practice supersedes SAE J1978 APR2002 and is technically equivalent to ISO 15031-4.
This document must undergo a Five-Year Review that is required by SAE for Recommended Practices. Changes that have been made to related SAE documents will also affect the content of this document, requiring changes herein. Additional changes and/or additions are also required in order to maintain the technical equivalency between this document and ISO 15031-4.
The committee shall increase customer satisfaction and lower product life cycle costs by investigating and recommending standards that will promote more effective diagnosis of vehicle electrical and electronic system problems. The resulting recommended practices will focus on model year 1992 and beyond. However, they may be useful for prior vehicle diagnosis/repair and may serve as a basis for additional recommended practices and pre-model year 1992 vehicles.Vision Statement: A standard disgnostic connector (in a standard location) will be in all vehicles. Pin assignments for a portion of the connector will also be standardized.All vehicles will implement a set of industry standard diagnostic test modes that can be executed over a standard communication data line (i.e., SAE J1850, ISO 9141-2). Industry standard test information will be associated with some of these diagnostic test modes.An OBD II scan tool will be able to utilize a minimum set of standardized diagnostic test modes and test information.A system will be in place that will allow standard electronic access of all E/E diagnostic service information. Future diagnostic legislation will be in harmony with this vision and the resulting SAE Recommended Practices.
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