ISO 15765-4:2021

Overview

ISO 15765-4:2021 - part of the ISO 15765 series on Diagnostic communication over Controller Area Network (DoCAN) - defines requirements for CAN‑based communication between a vehicle’s in‑vehicle network and the diagnostic link connector, specifically for emissions‑related systems. It specifies how CAN‑based systems should establish, maintain and terminate diagnostic communication with devices connected to the diagnostic link connector. The document does not prescribe in‑vehicle CAN network architecture; instead it focuses on protocol, timing, addressing and test‑equipment requirements needed to ensure interoperable emissions diagnostics.

Key Topics and Technical Requirements

• Scope of DoCAN for emissions: Requirements specific to On‑Board Diagnostics using OBDonUDS and OBDonEDS application protocols for emissions systems.
• OSI layering mapped to DoCAN: Requirements and framework for the Application, Session, Transport, Network, Data Link and Physical layers (layers 7–1 as applicable).
• Protocol identification: Procedures for vehicle and external test equipment to identify OBDonUDS and OBDonEDS operation modes.
• Bit rate validation: Procedures and records to validate CAN bit rates (including nominal bit rates such as 250 kbit/s and 500 kbit/s) and external test equipment timing.
• CAN identifier validation and addressing: Rules for mapping diagnostic addresses, functional vs. physical addressing, and handling of 11‑bit and 29‑bit CAN identifiers.
• Timing and flow control: Network layer timing parameters, flow control definitions and updated timeout values (notably changed timeout values to 33 ms in this edition).
• External test equipment (ETE) requirements: Electrical and cable parameters, interface propagation delays, and error detection provisions for diagnostic tools.
• Support for ECUNAME reporting: Requirements for reporting ECU identity strings to assist diagnostics and test equipment.
• Document changes in 2021 edition: Technical revisions include renaming of time‑related parameters and clarifications on acceptance of physically addressed request messages.

Applications - Who Uses ISO 15765-4:2021

• Automotive OEMs and ECU suppliers implementing compliant emissions diagnostic interfaces.
• Diagnostic tool and external test equipment manufacturers ensuring interoperability with vehicle diagnostics.
• Emissions testing labs and regulatory bodies verifying OBD communications during vehicle approval and inspection.
• Automotive test engineers and system integrators designing CAN‑based diagnostic links for emissions systems.

Practical benefits include standardized OBD communications for emissions compliance, reliable tool‑to‑vehicle interoperability, and clear electrical/timing requirements for test and service equipment.

Related Standards

• ISO 15765-2 (Transport protocol & network layer services)
• ISO 11898-1 / ISO 11898-2 (CAN data link and physical signalling)
• ISO 14229-2 (UDS session services)
• ISO 15031-3 (Diagnostic connector and related circuits)

Keywords: ISO 15765-4:2021, DoCAN, Diagnostic communication over CAN, OBDonUDS, OBDonEDS, emissions-related systems, diagnostic link connector, CAN identifier validation, bit rate validation, external test equipment.