Introduction to On Board Diagnostics (II)

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsSAE J 2012 standard defines the recommended practice for diagnostic trouble codes (DTC) ofall comprehensive components listed above. The DTC consists of an alpha-numericdesignator p0 - p3 for powertrain, , where p0 codes belong to SAE controlled codes, P1 belong tomanufacturer, and the rest are reserved for future use. The P0 codes care followed by three digitcodes assigned to individual faults. The assignment of the proper r designator should bedetermined by the PCM. In case of ambiguity, the upper most nibble of the two -byte codemessage as defined in SAE J 1979 will define the source system as follows: P0 - 0000, and P1 -0001. This standard defines diagnostic trouble codes for all the circuits, components, andsystems which are controlled by SAE, namely P0 codes. The P0 codes are defined by fourdifferent categories: General Circuit Malfunction, Range/Performance ance Problem, Low CircuitInput, and High Circuit Input. Manufacturers can define specific DTCs to meet their controlleralgorithms, but all DTC words must meet the terms’ definitions specified sin SAE J 1930standard for Diagnostic terms, definitions, abbreviations, and acronyms. aThe definition of thesefour categories of faults will be described first. Then the DTCs for different faults for eachsensor and actuator listed above will be described. SAE J 2012 provides guidance (definitions)for message formats, Parameter Identification numbers (PIDs(PIDs) ) and their definitions with actualexamples for compliance. The main aspects of these definitions are acovered below. For moredetailed knowledge of the DTCs and their messages, please refer to SAE J 2012, SAE J 1979, andSAE J 1930.