Overview
ISO 11992-4:2023 - "Road vehicles - Interchange of digital information on electrical connections between towing and towed vehicles - Part 4: Diagnostic communication" defines diagnostic application requirements and OSI-layer communication profiles to enable reliable diagnostic communication between towing and towed vehicles with a maximum authorized total mass greater than 3 500 kg. The document is structured around the OSI model and specifies application-, session-, transport-, network-, data link- and physical-layer requirements needed for diagnostic data exchange. Note: conformance and interoperability test plans are not included.
Key topics and technical requirements
The standard focuses on diagnostic communication over the vehicle-to-towed-vehicle electrical connection and includes:
- OSI-layer mapping and profiles - Application, Presentation, Session, Transport, Network, Data Link and Physical layer requirements and communication profiles (ComProfile).
- Application layer services - Diagnostic services such as CommunicationControl, ReadDataByIdentifier, ReadDtcInformation, DTC/DID definitions, negative response codes, and addressing of requested information.
- Abstract Service Primitive (ASP) - Definition of A_Data.req / A_Data.ind / A_Data.con interfaces and parameter mappings.
- Session & Transport layer definitions - Service primitives (S_Data, T_Data), transport protocol and USDT handling.
- Network layer requirements - Diagnostic CAN identifier configuration, dynamic and static network address assignment, gateway N_PDU routing and network address translation.
- Data link & Physical layer - CAN frame definitions and lower-layer requirements for robust link-level diagnostic exchange.
- Diagnostic elements - DTC field and functional unit definitions, Data Identifier (DID) structure and Diagnostic Communication Port (DCP).
- Structure and conformance notes - Introduction of requirement numbering, application requirements and OSI-specific clauses in this third edition.
Practical applications
ISO 11992-4:2023 is used to:
- Enable standardized remote diagnostics and maintenance data exchange between tractors and trailers (heavy trucks, buses, trailers, >3,500 kg).
- Support development of diagnostic tools, telematics gateways, and trailer electronic control units (ECUs) that interoperably read DIDs and DTCs.
- Guide OEM and supplier implementations for vehicle diagnostic interoperability across towing/towed interfaces.
- Define communication behavior for gateway routing, address assignment and session handling in multi-vehicle systems.
Who should use this standard
- Vehicle OEMs and trailer manufacturers
- ECU and telematics module suppliers
- Diagnostic tool and software developers
- Systems integrators and test engineers
- Standards committees and compliance managers
Related standards
Keywords: ISO 11992-4:2023, diagnostic communication, towing and towed vehicles, OSI layers, vehicle diagnostics, CAN, DTC, DID, network address assignment.
Open preview (PDF)Road vehicles — Interchange of digital information on electrical connections between towing and towed vehicles — Part 4: Diagnostic communication