ISO 27145-4:2017 — WWH-OBD — Part 4: Common Fault Diagnosis System

1. Scope and Connection Requirements for WWH-OBD

ISO 27145-4:2016 specifies the connection requirements between the vehicle and external test equipment for World-Wide Harmonized On-Board Diagnostics (WWH-OBD). This part of the ISO 27145 series covers the complete communication protocol stack from the physical layer through the application layer, ensuring that any compliant test equipment from any manufacturer can reliably communicate with any compliant vehicle. The standard addresses both wired CAN connections based on ISO 15765-4 and wired Ethernet connections based on ISO 13400 (DoIP), providing manufacturers with flexibility to choose the appropriate physical layer technology while maintaining full diagnostic interoperability across all vehicle platforms.

A fundamental requirement is that only one external test equipment at a time may be connected to the WWH-OBD-compliant vehicle’s diagnostic bus. This prevents conflicts between multiple diagnostic tools attempting simultaneous communication with the same ECUs. The standard specifies a comprehensive initialization sequence including bit-rate detection, address claiming to establish logical communication relationships, and WWH-OBD protocol validation to confirm that the vehicle supports the correct diagnostic protocol before any diagnostic services are initiated. This validation sequence prevents miscommunication with vehicles using legacy diagnostic protocols such as ISO 14230 (Keyword 2000) or SAE J1850.

2. Wired CAN and Ethernet Connection Specifications

For CAN-based communication, the standard specifies the complete protocol stack with detailed parameters for each layer. The CAN physical layer operates at 250 kbit/s or 500 kbit/s depending on the vehicle implementation, using standard 11-bit identifiers. The initialization sequence begins with bit-rate detection if the test equipment does not know the vehicle’s CAN bit rate, followed by the sending of a tester presence message to wake up ECUs from low-power sleep mode. The WWH-OBD protocol validation sequence involves the test equipment requesting vehicle identification information and confirming that the vehicle implements the ISO 27145 WWH-OBD protocol before proceeding with diagnostic services. This prevents communication attempts with vehicles using incompatible legacy protocols.

Diagnostic protocol timing parameters are precisely defined: P2 (server response time) is 50 milliseconds for standard responses and up to 5 seconds for responses requiring extended processing; P3 (client response time) is typically 5 milliseconds; and S3 (session timeout) is 5 seconds for default sessions and may be extended for programming sessions. The maximum number of WWH-OBD server ECUs on a single CAN bus segment is 16, which is sufficient for most vehicle architectures. Logical addressing uses predefined address ranges that distinguish between test equipment, vehicle ECUs, and functional broadcast addresses.

For Ethernet-based DoIP, the standard references ISO 13400 with WWH-OBD-specific adaptations. TCP port number 13400 is used for DoIP communication, with UDP port 13400 used for vehicle discovery messages. The DoIP initialization includes a vehicle discovery phase where the test equipment broadcasts a UDP discovery message and vehicles respond with their IP addresses and basic identification information. The routing activation procedure establishes communication pathways between the test equipment and specific target ECUs through the DoIP gateway. The Ethernet option enables significantly higher data rates compared to CAN — up to 100 Mbit/s — supporting faster software downloads and more data-intensive diagnostic procedures.

3. Engineering Insights for Diagnostic System Integration

The connection between vehicle and test equipment is the most critical interface in the entire diagnostic system architecture. Poor physical layer implementation can cause intermittent communication failures that are extremely difficult to diagnose — symptoms include occasional no-response errors, corrupted data frames, and timing violations that may only appear under specific environmental conditions. The standard requires specific protection circuitry on the diagnostic pins including short-circuit protection to battery and ground, overvoltage protection against load dump transients that can reach 50 V or more, and electrostatic discharge protection per ISO 10605. The diagnostic connector must withstand a minimum of 1000 insertion/removal cycles without degradation.

The diagnostic connector pin assignment follows ISO 15031-3 for the 16-pin OBD connector, ensuring backward compatibility with existing OBD-II scan tools. However, WWH-OBD uses different communication parameters and protocol sequences than traditional OBD-II — the hardware connector is the same but the software protocol is different. Scan tools must detect which protocol the vehicle supports and adapt accordingly. For DoIP implementations, specific pins in the 16-pin connector are assigned for Ethernet signals, including a dedicated activation line that signals the vehicle’s DoIP gateway to power up its Ethernet interface. The standard also specifies cable length limits, termination requirements, and signal quality parameters for both CAN and Ethernet physical layers.

The standard’s requirements are organized to support both CAN and Ethernet implementations within a common framework, allowing manufacturers to standardize their diagnostic architecture while choosing the physical layer best suited to their vehicle platform. Development and validation of the connection layer requires thorough testing with multiple test equipment implementations to verify interoperability. The standard provides test procedures and pass-fail criteria for each layer of the protocol stack, enabling systematic compliance testing. Automotive suppliers implementing WWH-OBD in ECUs and gateway modules should participate in interoperability testing events organized by standards bodies or industry consortia.

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