This SAE Recommended Practice is applicable to all light-duty gasoline and diesel passenger vehicles and trucks, and to heavy-duty gasoline vehicles. Specific applications of this document include diagnostic, service and repair manuals, bulletins and updates, training manuals, repair databases, underhood emission labels, and emission certification applications. This document focuses on diagnostic terms applicable to electrical/electronic systems, and therefore also contains related mechanical terms, definitions, abbreviations, and acronyms. Even though the use and appropriate updating of this document is strongly encouraged, nothing in this document should be construed as prohibiting the introduction of a term, abbreviation or acronym not covered by this document. Certain terms have already been in common use and are readily understood by manufacturers 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, "historically acceptable common 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.; and 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.)