The SAE J1939 series of recommended practices are intended for light- and heavy-duty vehicle uses on- or off-road as well as appropriate stationary applications which use vehicle derived components (e.g., generator sets). Vehicles of interest include, but are not limited to: on- and off-highway trucks and their trailers, construction equipment, and agriculture equipment and implements. The purpose of these documents is to provide an open interconnect system for on-board electronic systems. It is the intention of these documents to allow electronic devices to communicate with each other by providing a standard architecture. J1939-73 identifies the diagnostic connector to be used for the vehicle service tool interface and defines messages to accoumplish diagnostic services. California-regulated OBD II requirements are satisfied with a subset of the specified connector and the defined messages. Diagnostic messages (DMs) provide the utility needed when the vehicle is being repaired. Diagnostic meassages are also used during vehicle operation by the netwroked electronic control modules to allow them to report diagnostic information and self-compensate as appropriate, based on information received. Diagnostic messages include services such as periodically broadcasting active diagnostic trouble codes, identifiying operator diagnostic lamp status, reading or clearing diagnostic trouble codes, reading or writing control module memory, provide a security function, stopping/starting message broadcasts, reporting diagnostic readiness, monitoring engine parametric data, etc.