Road vehicles — Interchange of digital information on electrical connections between towing and towed vehicles — Part 4: Diagnostic communication
1Key Takeaways
This document specifies diagnostic application requirements and OSI-layer related communication profiles to ensure the interchange of digital information between towing and towed vehicles with a maximum authorized total mass greater than 3500 kg. The conformance and interoperability test plans are not part of this docu…
2Expert Interpretation
Professional interpretation of ISO 11992-4:2023 international standard, covering the digital information exchange specifications for heavy-duty vehicle traction and trailer workshops. Detailed analysis of diagnostic communication architecture, OSI layering requirements, data identifier definitions and network address translation mechanisms, providing implementation guidelines in compliance with SAE J1939 and UDSonCAN.
Analysis of the core content of the standard
The third edition of ISO 11992-4:2023 replaces the 2014 edition of the standard. The main updates include:
- Introduction of a numbered and named requirement structure system
- Added application layer requirement specifications
- Clarified OSI layering technical requirements
- Deleted subnet addressing clauses and optimized gateway address translation mechanism
Communication architecture and technical specifications
| OSI layering | Key technologies | Follow the standards |
|---|---|---|
| Application layer | UDS diagnostic service, DID definition, DTC functional unit | ISO 14229-1/3 |
| Transport Layer | USDT Unconfirmed Segmented Transmission | ISO 15765-2 |
| Network Layer | Dynamic/Static Address Allocation, NAT Translation | ISO 15765-5 |
| Data Link Layer | CEFF Extended Frame Format | SAE J1939-21 |
Key Diagnostic Service Implementation
Data Identifier (DID) Specification
The standard mandates the implementation of the following basic DIDs:
- F00116: Braking and traveling mechanism remote address configuration data
- F19016: Vehicle identification number (VIN)
- F18D16: List of supported functional units
Diagnostic trouble code (DTC) structure
The DTC field contains 5 key elements:
- Severity (DTCSeverity)
- Functional unit identifier (0x01-0x19 corresponds to different systems)
- Basic fault code (DTCRecord)
- Fault type (DTCFailureType)
- Status flag (StatusOfDTC)
Network Address Translation Mechanism
The standard defines a three-level address translation system:
| Communication direction | Address translation rules |
|---|---|
| Tractor→Trailer | Keep the source/destination address and extend the network identifier through the AE field |
| Gateway→In-vehicle network | AE field is converted to the target address, and the source address is fixed to 0x01/0x02 |
| ECU response path | Reverse mapping SA/TA and carrying the original client AE |
Typical diagnostic message routing requires 5 address translations (2 requests + 3 responses)
Implementation recommendations
Key points of compatibility design
- The physical layer must comply with the 250kbps CAN bus specification defined in ISO 11992-1
- The diagnostic connector (DLC) should support a 29-bit extended identifier
- It is prohibited to disable normal communication through the CommunicationControl service during driving
Timing parameter configuration
Key timing parameters should comply with:
- Server response timeout (P2_Server): ≤50ms (regular request)
- Client waiting timeout (P2_Client): ≥250ms
- Segmented transmission interval (STmin): 10-127ms