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SAE J1979 (MAY2025)

E/E Diagnostic Test Modes
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SAE J1979 (MAY2025)

E/E Diagnostic Test Modes

PUBLISH DATE 2025
SAE J1979 (MAY2025)

SAE J1979/ISO 15031-5 set includes the communication between the vehicle’s OBD systems and test equipment implemented across vehicles within the scope of the legislated emissions-related OBD.

To achieve this, it is based on the Open Systems Interconnection (OSI) Basic Reference Model in accordance with ISO/IEC 7498-1 and ISO/IEC 10731, which structures communication systems into seven layers. When mapped on this model, the services specified are broken into:

  • Diagnostic services (layer 7), specified in:
    • ISO 15031-5/SAE J1979 (emissions-related OBD),
    • ISO 27145-3 (WWH-OBD),
  • Presentation layer (layer 6), specified in:
    • ISO 15031-2, SAE J1930-DA,
    • ISO 15031-5, SAE J1979-DA,
    • ISO 15031-6, SAE J2012-DA,
    • ISO 27145-2, SAE J2012-DA,
  • Session layer services (layer 5), specified in:
    • ISO 14229-2 supports ISO 15765-4 DoCAN and ISO 14230-4 DoK-Line protocols,
    • ISO 14229-2 is not applicable to the SAE J1850 and ISO 9141-2 protocols,
  • Transport layer services (layer 4), specified in:
    • DoCAN: ISO 15765-2 Transport protocol and network layer services,
    • SAE J1850: ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
    • ISO 9141-2: ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
    • DoK-Line: ISO 14230-4, ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
  • Network layer services (layer 3), specified in:
    • DoCAN: ISO 15765-2 Transport protocol and network layer services,
    • SAE J1850: ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
    • ISO 9141-2: ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
    • DoK-Line: ISO 14230-4, ISO 15031-5/SAE J1979 Emissions-related diagnostic services,
  • Data link layer (layer 2), specified in:
    • DoCAN: ISO 15765-4, ISO 11898-1, -2,
    • SAE J1850,
    • ISO 9141-2,
    • DoK-Line: ISO 14230-2,
  • Physical layer (layer 1), specified in:
    • DoCAN: ISO 15765-4, ISO 11898-1, -2,
    • SAE J1850,
    • ISO 9141-2,
    • DoK-Line: ISO 14230-1,

in accordance with Table 1.

The primary purpose of SAE J1979 (also known as OBD-II) is to establish a standardized way for vehicles to communicate diagnostic data with external test equipment.

This data, accessed via a scan tool, allows technicians and others to diagnose and troubleshoot vehicle issues related to emissions and other regulated systems.

In essence, it ensures a consistent and standardized approach to accessing vehicle diagnostic information across various makes and models.

SDO SAE: SAE International
Document Number J1979
Publication Date May 23, 2025
Language en - English
Page Count 143
Revision Level 202505
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