Purpose - 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.

Differences from ISO Document - The ISO 15031-4 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.

Notable exceptions are:

a. Proposed U.S. OBD regulations will allow 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.

b. Proposed 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 needs to be supported by an SAE J1978 diagnostic scan tool.

Differences between the documents are highlighted in the technical requirements sections of this document. Deleted text is highlighted with struck through and new text is highlighted with bold italic.

NOTE - To maintain equivalency of the documents, a comma is used as a decimal marker for numeric values in this document.

Customers who purchased SAE J1978
also purchased

• SAE J1930DA : J1930 Electrical/Electronic Systems Diagnostic Terms, Definitions, Abbreviations, and Acronyms Web Tool Spreadsheet-See Also SAE J1930
• SAE J1979 : E/E Diagnostic Test Modes
• SAE J1850 : Class B Data Communications Network Interface
• SAE J1962 : (R) Diagnostic Connector Equivalent to ISO/DIS 15031-3:December 14, 2001

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