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 also 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: a) the DTC format, which consists of: 1) addressing format; 2) structure; 3) messages; b) a standardized set of DTC and descriptions; c) a standardized set of DTC subtypes known as failure types.This part of ISO 15031 specifies all general rules and guidelines to define new DTCs. This part of ISO 15031 references the SAE J2012-DA (Digital Annex), which includes all standardized DTCs (number and text descriptor) as well as all DTC subtypes known as failure types.