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.