This SAE Information Report describes the diagnostic data communications required for implementation of a set of diagnostic test modes for all electronic systems on the vehicle's serial data link. These test modes can be used by off-board test equipment for both service and assembly plant testing. The goal of this document is to provide standard methods to perform common functions for all electronic systems. This standard set of procedures will aid development, production, and field service of those systems. Use of the standard data communications in this specification will potentially result in the following benefits: Common methods and procedures for developers to use, without the need to invent methods to perform these functions; Common programming techniques for system programmers, with increased sharing of software procedures; Common hardware, software and test procedures for assembly plant testing; Common hardware, software and service procedures for service diagnostics across different vehicle manufacturers and systems. This specification includes: Diagnostic Message Formats, Device ID's, Functional descriptions of all diagnostic test modes, Message and response formats for all diagnostic test modes.