ISO 27145-6:2017 — WWH-OBD — Part 6: External Test Equipment

1. Scope and Overview of External Test Equipment Requirements

ISO 27145-6:2023 specifies functional requirements for external test equipment used with World-Wide Harmonized On-Board Diagnostics (WWH-OBD) systems. This part defines what diagnostic scan tools and test devices must do when communicating with WWH-OBD-compliant vehicles, covering mechanical design, electrical characteristics, communication setup procedures, diagnostic message handling, data information management, and diagnostic trouble code (DTC) processing. The standard establishes a common framework ensuring that diagnostic tools from any manufacturer can perform consistent, reliable vehicle diagnostics across different vehicle makes and models.

The standard organizes requirements into clusters that group related functional areas, making it easier for developers to implement and verify compliance. The mechanical requirements cluster covers connector durability, cable length, and housing protection ratings. The electrical cluster defines voltage ranges, current limits, and protection circuitry. The communication setup cluster specifies protocol detection, session establishment, and ECU addressing procedures. The diagnostic messages cluster addresses timing requirements, negative response handling, and error management strategies. The data information cluster covers parameter identification, scaling factors, and unit conversion rules. The DTC processing cluster specifies reading, clearing, and status tracking procedures.

2. Specific Requirements for Test Equipment Functionality

The standard requires external test equipment to automatically detect the communication protocol used by the vehicle upon connection — distinguishing between CAN-based WWH-OBD, DoIP-based WWH-OBD, and legacy protocols — and establish an appropriate diagnostic session. The test equipment must enumerate all WWH-OBD-compliant ECUs present on the vehicle network and present them to the user for selection. The automatic discovery process uses functional addressing to request vehicle identification from all ECUs simultaneously, building a complete list of available diagnostic servers. This ECU list is the foundation for all subsequent diagnostic operations.

Diagnostic message handling requirements include proper responses to all possible negative response codes. When an ECU responds with requestCorrectlyReceived-ResponsePending (negative response code 0x78), the test equipment must wait for the ECU to complete its processing and send the actual response rather than timing out or reporting an error prematurely. For no-response situations, the standard specifies a retry strategy with defined maximum retry counts and timeout values, after which the user must be notified of the communication failure. The equipment must not enter infinite retry loops — this could drain the vehicle battery during diagnostic sessions or confuse ECU diagnostic state machines.

DTC information list management requires supporting multiple status reporting formats: confirmed DTCs indicating active fault conditions requiring repair, pending DTCs for faults detected during the current or most recent driving cycle that have not yet met confirmation criteria, and permanent DTCs that remain stored even after clearing attempts until the fault is repaired and verified. The test equipment must also be capable of reading freeze frame data — a snapshot of vehicle operating conditions at the time of fault detection — including engine speed, vehicle speed, coolant temperature, fuel system status, and other parameters defined in the common data dictionary.

3. Engineering Insights for Diagnostic Tool Development

Developing WWH-OBD-compliant test equipment requires careful implementation of the complete communication protocol stack defined across all parts of ISO 27145. The requirements clustering approach helps developers organize implementation work by functional area and prioritize features based on their target market and product positioning. A basic code reader may only need to implement the mechanical, electrical, communication setup, and DTC processing clusters, while a comprehensive diagnostic scan tool must implement all clusters including diagnostic message handling with full negative response management and data information management with complete parameter identification and scaling.

User interface considerations are also addressed by the standard’s emphasis on clear, understandable presentation of diagnostic information. The standard recommends avoiding unnecessarily complex technical jargon that might confuse operators who are not diagnostic specialists. Test results should be presented with clear pass-fail indications, DTC descriptions should include both the standardized code and human-readable text explaining the fault condition, and freeze frame data should be displayed with parameter names, current values, and engineering units in an organized tabular format. The equipment should provide guidance on possible causes and recommended repair actions based on the diagnostic results obtained.

The standard requires that user instructions and equipment documentation clearly explain the equipment’s capabilities and limitations. Users must understand what diagnostic functions are supported, what vehicle models and model years are compatible, and what the equipment cannot do. This is particularly important for aftermarket diagnostic tools used by independent repair facilities that may need to diagnose a wide variety of vehicle makes and models. The standard also addresses requirements for future updates and upgrades — test equipment should be designed with updatable firmware to accommodate new vehicle models, revised diagnostic protocols, and additional features as the WWH-OBD standard continues to evolve.

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