This part of ISO 15031 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.This part of ISO 15031 specifies the rules and guidelines for the definition of the following:a) the diagnostic trouble code format, which consists of the following:1) addressing format;2) structure;3) 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;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).This part of ISO 15031 specifies all general rules and guidelines to define new diagnostic trouble codes. This part of ISO 15031 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.