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ISO 27145-1:2012 – WWH-OBD Communication: General Information and Use Case Definition
Understanding the framework for World-Wide Harmonized On-Board Diagnostics communication requirements
Introduction to ISO 27145-1:2012
ISO 27145-1:2012 is the foundational document of the ISO 27145 series, which establishes the communication framework for World-Wide Harmonized On-Board Diagnostics (WWH-OBD). This standard, prepared by ISO/TC 22 (Road vehicles) Subcommittee SC 3, provides the general information and use case definitions that underpin the entire WWH-OBD communication architecture.
The WWH-OBD system is designed to enable standardized communication between a vehicle’s on-board diagnostic systems and external (off-board) generic test equipment, supporting global regulatory requirements for emissions monitoring and vehicle diagnostics. This first edition cancels and replaces ISO/PAS 27145-1:2006.
ISO 27145-1 serves as the entry point for understanding the entire WWH-OBD standards family. Before diving into the detailed data dictionary (Part 2) or message specifications (Part 3), reading Part 1 provides the essential context and architectural overview needed to navigate the series effectively.
WWH-OBD Architecture and OSI Model Integration
The ISO 27145 series is structured around the Open Systems Interconnection (OSI) Basic Reference Model (ISO/IEC 7498-1 and ISO/IEC 10731), which divides communication systems into seven distinct layers. This layered approach ensures modularity, interoperability, and clear separation of concerns across the diagnostic communication stack.
| OSI Layer | Function | WWH-OBD Reference |
|---|---|---|
| 7 – Application | Diagnostic services | ISO 14229-1, ISO 27145-3 |
| 6 – Presentation | Data encoding and formatting | ISO 27145-2, SAE J1930-DA, SAE J1979-DA, SAE J2012-DA |
| 5 – Session | Session management | ISO 14229-2 |
| 4 – Transport | End-to-end data transport | ISO 15765-2 (DoCAN), ISO 13400-2 (DoIP), ISO 27145-4 |
| 3 – Network | Routing and addressing | ISO 15765-2, ISO 15765-4, ISO 13400-2, ISO 27145-4 |
| 2 – Data Link | Frame transmission and error detection | ISO 11898-1, ISO 11898-2, ISO 15765-4, ISO 13400-3, IEEE 802.3 |
| 1 – Physical | Electrical and mechanical interface | ISO 11898-1, ISO 11898-2, ISO 15765-4, ISO 13400-3, IEEE 802.3 |
A key innovation of the WWH-OBD architecture is its support for multiple physical transport technologies. The standard accommodates both CAN-based diagnostics (DoCAN — ISO 15765-4) and IP-based diagnostics (DoIP — ISO 13400-2), allowing vehicle manufacturers to choose the most appropriate communication technology for their platform while maintaining a unified diagnostic service interface at the application layer.
The dual-transport approach (DoCAN + DoIP) in WWH-OBD provides backward compatibility with existing CAN-based diagnostic tools while enabling the higher bandwidth and more flexible networking capabilities of Ethernet-based diagnostics for next-generation vehicles. This design choice future-proofs the standard for evolving automotive network architectures.
WWH-OBD Use Case Definition
ISO 27145-1 defines three primary use case clusters that represent the core diagnostic interaction scenarios between the vehicle and external test equipment. These use cases form the functional foundation of the WWH-OBD system.
Use Case Clusters
| Use Case | Description | Key Data Elements |
|---|---|---|
| UC 1 — OBD System State | Information about the emissions-related OBD system state | OBD readiness status, monitor completion status, MIL status |
| UC 2 — Active Malfunctions | Information about active and confirmed emissions-related malfunctions | Diagnostic Trouble Codes (DTCs), freeze frame data, pending codes |
| UC 3 — Diagnosis for Repair | Information related to diagnosis for the purpose of repair | Live data parameters, actuator tests, ECU identification |
These use cases are designed to align with the regulatory requirements of the WWH-OBD Global Technical Regulations (GTR) established under the United Nations Economic Commission for Europe (UNECE). Each use case defines a specific set of diagnostic services and data elements that external test equipment can request from the vehicle’s OBD system.
Use case UC 3 (Diagnosis for Repair) provides access to a wider range of diagnostic data than UC 1 or UC 2. Access to this use case may be restricted by vehicle manufacturers for security or intellectual property reasons. The standard allows for implementation-specific access control mechanisms while maintaining the core communication protocol.
Vehicle On-Board Diagnostics (VOBD) Definition
ISO 27145-1 introduces the concept of the Vehicle On-Board Diagnostics (VOBD) system as the on-vehicle implementation of the WWH-OBD requirements. The VOBD system comprises three key elements: the VOBD definition, the VOBD data set, and the VOBD access method.
The VOBD definition establishes which diagnostic data elements and services are available on a particular vehicle implementation. The VOBD data set defines the specific data parameters, diagnostic trouble codes, and monitor identifiers that the vehicle supports. The VOBD access method specifies how external test equipment establishes communication with the vehicle’s diagnostic system.
This three-part structure ensures that the WWH-OBD framework is flexible enough to accommodate different vehicle platforms and emissions control strategies while maintaining a consistent external interface for generic test equipment.
When developing external test equipment for WWH-OBD compliance, pay careful attention to the VOBD access method negotiation sequence. The vehicle and test equipment must agree on the communication protocol variant (DoCAN or DoIP), timing parameters, and addressing scheme before diagnostic data exchange can begin.
Engineering Design Insights
Implementing WWH-OBD communication requires careful attention to the interaction between the OSI layers. From an engineering perspective, the presentation layer (Layer 6) defined in ISO 27145-2 is particularly critical because it handles the encoding and decoding of all diagnostic data. The standard’s reference to SAE digital annexes (J1979-DA, J2012-DA, J1930-DA) means that data definitions are maintained separately from the protocol specification, allowing for rapid updates as new diagnostic parameters are needed.
The session layer (Layer 5, ISO 14229-2) manages diagnostic session states including default session, programming session, and extended diagnostic session. WWH-OBD primarily operates in the default diagnostic session for basic emissions-related diagnostics, but may require extended sessions for advanced repair functions (UC 3).
For vehicle manufacturers, implementing the full ISO 27145 series requires integration with existing diagnostic implementations. The standard’s alignment with ISO 14229-1 (Unified Diagnostic Services, UDS) means that many WWH-OBD functions map directly to existing UDS services, reducing implementation complexity for manufacturers already using UDS-based diagnostics.
A common pitfall in WWH-OBD implementation is inadequate handling of timing requirements. The DoCAN transport protocol (ISO 15765-2) and DoIP protocol (ISO 13400-2) have very different timing characteristics. Test equipment must be designed to handle both timing regimes appropriately, including proper timeout handling and flow control for segmented messages.
Frequently Asked Questions
Q1: What is the relationship between ISO 27145-1 and the WWH-OBD GTR?
A: ISO 27145-1 implements the communication requirements specified by the World-Wide Harmonized On-Board Diagnostics Global Technical Regulations (WWH-OBD GTR) established by UNECE. The standard translates regulatory requirements into technical specifications for the communication interface between vehicles and diagnostic test equipment.
A: ISO 27145-1 implements the communication requirements specified by the World-Wide Harmonized On-Board Diagnostics Global Technical Regulations (WWH-OBD GTR) established by UNECE. The standard translates regulatory requirements into technical specifications for the communication interface between vehicles and diagnostic test equipment.
Q2: How does WWH-OBD differ from the OBD-II standard used in the United States?
A: WWH-OBD (ISO 27145 series) is a global harmonized standard that aims to unify various regional OBD requirements (US OBD-II, European EOBD, Japanese JOBD, etc.) under a single communication framework. While OBD-II is primarily based on SAE J1962/J1979, WWH-OBD references the same SAE data dictionaries while adding a more formalized OSI-layered architecture and support for both CAN and IP transport.
A: WWH-OBD (ISO 27145 series) is a global harmonized standard that aims to unify various regional OBD requirements (US OBD-II, European EOBD, Japanese JOBD, etc.) under a single communication framework. While OBD-II is primarily based on SAE J1962/J1979, WWH-OBD references the same SAE data dictionaries while adding a more formalized OSI-layered architecture and support for both CAN and IP transport.
Q3: What parts make up the complete ISO 27145 series?
A: The series consists of Part 1 (general information and use cases), Part 2 (common data dictionary), Part 3 (common message dictionary), Part 4 (connection between vehicle and test equipment), and Part 6 (external test equipment, under preparation as of the 2012 edition).
A: The series consists of Part 1 (general information and use cases), Part 2 (common data dictionary), Part 3 (common message dictionary), Part 4 (connection between vehicle and test equipment), and Part 6 (external test equipment, under preparation as of the 2012 edition).
Q4: Is ISO 27145-1 applicable to electric vehicles?
A: Yes, the WWH-OBD framework is designed to be technology-neutral and applies to all road vehicles, including electric vehicles (EVs) and hybrid electric vehicles (HEVs). The emissions-related diagnostic requirements for EVs focus on the traction battery management system, electric drive monitoring, and charging system diagnostics rather than conventional tailpipe emissions.
A: Yes, the WWH-OBD framework is designed to be technology-neutral and applies to all road vehicles, including electric vehicles (EVs) and hybrid electric vehicles (HEVs). The emissions-related diagnostic requirements for EVs focus on the traction battery management system, electric drive monitoring, and charging system diagnostics rather than conventional tailpipe emissions.
