Introduction to On Board Diagnostics (II)

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Detailed Header Formats and PhysicalAddress Segments: (SAE J 2178/1):SAE J 2178/1, is the Class B Data Communication Network Messages’ s’ Detailed Header formatsand Physical Address Assignments specification. The standard defines the informationcontained in the header and data fields of non-diagnostic messages. The standard also specifiesfield sizes, scaling, representations, and data positions used within messages. The generalstructure of the message frame is described with inframe response included in Figure 1 andwithout the response in Figure 2 of the standard. SAE J 1979 standard defines the informationcontained in the header and data fields of emission related diagnostic messages. SAE J 2190standard defines the information contained in the header and data a fields of other diagnosticmessages not related to emissions. SAE J 1850 standard defines the class B network interfacehardware, basic protocol definition, the electrical specifications, and the error detection-correction scheme using CRC (cyclic redundancy check) Byte. SAE J 1850 defines only twomessage formats. They are the single Byte format and the consolidated header format. Theconsolidated header format has two forms: a single Byte form, and d a three byte form. Thisstandard covers all these formats and forms to identify the contents of messages which can besent on the SAE J 1850 network.