E/E Diagnostic Test Modes: OBDonUDS
J1979-2_202104
SAE J1979-2 describes the communication between the vehicle's OBD systems and test equipment required by OBD regulations. On-Board Diagnostic (OBD) regulations require passenger cars and light-, medium-, and heavy-duty trucks to support a minimum set of diagnostic information to external (off-board) “generic” test equipment.
To achieve this, SAE J1979-2 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 14229-1
○
SAE J1979-2 OBDonUDS
Presentation layer (layer 6), specified in:
○
SAE J1930, SAE J1930DA
○
SAE J1979DA
○
SAE J2012, SAE J2012DA
○
SAE J1939DA, SAE J1939-73
Session layer services (layer 5), specified in:
○
ISO 14229-2
Transport layer services (layer 4), specified in:
○
DoCAN: ISO 15765-2 Transport protocol and network layer services
○
ISO 15765-4
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DoIP: ISO 13400-2 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 2:Transport protocol and network layer services
Network layer services (layer 3), specified in:
○
DoCAN: ISO 15765-2 Transport protocol and network layer services
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ISO 15765-4 Requirements for emissions related systems
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DoIP: ISO 13400-2 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 2:Transport protocol and network layer services
Data link layer (layer 2), specified in:
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DoCAN: ISO 15765-4, ISO 11898-1, -2
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DoIP: ISO 13400-3 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 3: Wired vehicle interface based on IEEE 802.3
Physical layer (layer 1), specified in:
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DoCAN: ISO 15765-4, ISO 11898-1, -2, in accordance with Table 1
○
DoIP: ISO 13400-3 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 3: Wired vehicle interface based on IEEE 802.3
Rationale:
Due to regulatory adoption of OBDonUDS, SAE J1979 now becomes a multiple part document series:
1
SAE J1979, which defines diagnostic test modes for legacy data links used for emissions OBD (e.g., SAE J1850, ISO 9141-2, ISO 14230-4, ISO 15765-4).
2
SAE J1979-2, which defines the latest diagnostic services for OBDonUDS used for emissions OBD (e.g., ISO 14229-1).
Market regulations specify which data links are allowed for sale in a given market.
OBDonUDS is not just a translation of the classic SAE J1979 $01-$0A services to UDS services—it provides extra features: DTC based Readiness, ExtendedDataRecords for DTCs, Readiness group to DTC readiness translation, and support for snapshots for up to five DTCs and two occurrences each. Other clarifications and functional enhancements are also included in this document.
Included in: On-Board Diagnostics for Light and Medium Duty Vehicles Subscription Learn More
Related Topics:
Electrical systems
Electronic control units
Engine control systems
On-board diagnostics (OBD)
Light trucks
Control systems
Electronic control systems
Emissions control
Communication protocols
Test equipment and instrumentation
Also known as: SAE J 1979-2
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