ISO 15031-6:2015 provides uniformity for standardized diagnostic trouble codes (DTC) that electrical/electronic On-Board Diagnostic (OBD) systems of motor vehicles are required to report when malfunctions are detected. It further provides guidance for uniform messages (text descriptor) associated with these codes.

ISO 15031-6:2015 specifies the rules and guidelines for the definition of the following: a) the diagnostic trouble code format, which consists of addressing format, structure and messages; b) a description of the standardized set of diagnostic trouble codes and descriptions contained in SAE J2012-DA. The two most significant bytes of a DTC may be decoded according to two different lists in two formats: DTC Format Identifier 00₁₆ and 04₁₆; and c) a description of the standardized set of diagnostic trouble codes subtypes known as failure types contained in SAE J2012-DA (applies only when 3-byte DTCs are used).

ISO 15031-6:2015 specifies all general rules and guidelines to define new diagnostic trouble codes. It references SAE J2012-DA (Digital Annex), which includes all standardized DTCs (number and text descriptor) as well as all diagnostic trouble codes subtypes known as failure types.