ISO 15031-6:2015

Overview

ISO 15031-6:2015 - Road vehicles: Communication between vehicle and external equipment for emissions-related diagnostics - Part 6: Diagnostic trouble code definitions - defines a uniform, industry‑wide approach to Diagnostic Trouble Codes (DTCs) used by On‑Board Diagnostic (OBD) systems. It specifies the DTC format, text descriptors, and the rules for creating and registering new codes, and it references the SAE J2012‑DA digital annex that contains the standardized DTC register and failure‑type definitions.

Key Topics and Technical Requirements

• DTC format and structure: Rules for addressing, byte structure and message content for OBD DTCs. The two most significant bytes of a DTC can be decoded using different lists identified by DTC Format Identifiers (e.g., 00 and 04 in hexadecimal).
• Three‑byte DTCs and failure types: Guidance for the optional third byte (failure type byte, FTB) and standardized subtypes (failure categories) as defined in SAE J2012‑DA.
• Text descriptors: Guidance for uniform human- and machine‑readable text descriptors associated with each DTC to ensure consistent messaging across tools and manufacturers.
• System groupings: Classification of DTCs by system domain - powertrain, body, chassis, network/vehicle integration - to support organized diagnostics.
• Sensor location and naming: Definitions and conventions for sensor location identifiers (examples include multi‑bank engine/catalyst layouts), and naming guidelines (referencing SAE J1930 and SAE J2012 conventions).
• Rules for new codes: Procedures and general rules to define and request additions or revisions to the standardized DTC register via the SAE J2012‑DA revision process.

Practical Applications and Who Uses This Standard

ISO 15031-6:2015 is essential for stakeholders involved in vehicle emissions diagnostics and OBD tool interoperability:

• Automotive OEMs and Tier suppliers - to implement standardized DTCs and descriptors in vehicle ECUs.
• Diagnostic tool and scan‑tool manufacturers - to decode, display and interpret standardized DTCs for service technicians.
• Repair shops and service technicians - to interpret DTCs consistently across vehicle makes and models.
• Regulatory bodies and certification labs - to verify emissions‑related OBD compliance and reporting.
• Telematics and fleet management providers - to integrate consistent fault reporting into remote diagnostics systems.

Related Standards and References

• SAE J2012‑DA (Digital Annex): authoritative register of standardized DTC numbers, text descriptors and failure types referenced by ISO 15031‑6.
• ISO 15031 series: Parts 1–7 cover related topics (general info, connector specs, diagnostic services, data link security).
• SAE J1930 / J1979: naming and diagnostic service references used in conjunction with ISO 15031‑6.

ISO 15031-6:2015 enables consistent emissions-related diagnostics by standardizing how faults are coded, described and managed across tools and vehicles - improving interoperability, repair accuracy, and regulatory compliance.