Introduction to On Board Diagnostics (II)

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsCore DTCS: Core DTCs are those codes which have achieved compliance uniformlythroughout the industry. For these, a common DTC number, and fault message is assigned.Undefined DTCs are reserved for future use. Even though the service procedures forrectifying each of these DTCs may vary among manufacturers, the fault indicated bythe DTC is common enough to be assigned a particular fault code.Non-Uniform DTC: These are fault codes that have very little commonality amongmanufacturers due to system differences, implementation differences, or diagnosticstrategy differences. Manufacturers who define their own DTCs in this area areurged to remain consistent across their product line when assigning codes in manufacturercontrolled area. Same groupings should be used as in SAE controlled area, i.e.., 100s and 200sfor fuel and air metering, 300 for ignition system or misfire, etc.Each defined DTC is assigned a message to indicate the circuit, component, or system areathat is faulty. The messages are organized such that different messages related to aparticular sensor or system are grouped together. In cases where there are various faultmessages for different types of faults, the group also has a “Generic” message as the faultCode/Message of the group. Manufacturer has a choice to use the specific or generic faultcode, provided only one code is used consistently to describe that fault.