This SAE Recommended Practice is applicable to all E/E systems on MD and HD vehicles. The terms defined are largely focused on compression-ignited and spark-ignited engines. Specific applications of this document include diagnostic, service and repair manuals, bulletins and updates, training manuals, repair data bases, under-hood emission labels, and emission certification applications. This document focuses on diagnostic terms, definitions, abbreviations, and acronyms applicable to E/E systems. It also covers mechanical systems which require definition. Nothing in this document should be construed as prohibiting the introduction of a term, abbreviation, or acronym not covered by this document. The use and appropriate updating of this document is strongly encouraged. Certain terms have already been in common use and are readily understood by manufactureres and technicians, but do not follow the methodology of this document. To preserve this understanding, these terms were included and have been identified with the footnote (2), "previous usage," so they will not erroneously serve as a precedent in the construction of new names. These terms fall into three categories: a. Acronyms that do not logically fit the term. b. Acronyms existing at the component level, i.e., their terms contain the base word or noun that describes the generic item that is being further defined. c. Acronyms for terms that appear to contain the base word, but are frequently used as a modifier to another base word. (This use may possibly be thought of as following the methodology since the acronym is normally used as a modifier.)