Introduction to On Board Diagnostics (II)

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Data Parameter Defintions: : (SAE J2178/2):SAE J 2178/2 Data Parameter Definitions standard defines the parameters ameters used todescribe the data variables used in normal vehicle operation as well as diagnosticoperation. Parameters are assigned Parameter Reference Numbers (PRNs(PRNs) ) which aredescribed in the standard. PRN structure is shown in Figure 3 in the standard. Thesecond part of the parameter definition is the SLOT. PRN identifies ies a specificparameter by name, unit measure , and its associated SLOT. The SLOT Sdefines themathematical characteristic of parameters in terms of its numeric presentation, itsscaling, its limits, Offsets, and its transfer function.Appendix A and B provide cross references to find the PRN by the number or byname. PRN structure is given in Figure 3. SAE J 1979 refers to PID Pnumbers whichare single byte reference number. The first 256 PRNs defined in this standard areidentical to the SAE J 1979 PID definitions. The standard contains ns detailed lists ofPRN assignments which are used for reference.