ISO 11992-4:2023

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

• ISO 11992 series (Parts 1–3) for vehicle-to-towed-vehicle communications
• ISO 14229 (UDS) series for diagnostic services
• ISO 22901-1 (vehicle-specific diagnostic data) and ISO/IEC 7498-1 (OSI reference model)

Keywords: ISO 11992-4:2023, diagnostic communication, towing and towed vehicles, OSI layers, vehicle diagnostics, CAN, DTC, DID, network address assignment.