OBD-II Subaru Diagnostic Systems:

Diagnostic Trouble Codes (DTC) Display:

OBD-II regulations require the use of standardized DTCs. There’s no longer a need to learn the diagnostic language of individual vehicle manufacturers. Diagnostic Trouble Code (DTC) definitions and numbers were prescribed by the Society of Automotive Engineers (SAE) under J2012.

Powertrain DTCs beginning with the prefix “P0” have standardized meanings and may be used by all vehicle manufacturers. Powertrain DTCs beginning with the prefix “P1” are considered “manufacturer specific” and may be used to define systems or functions that are unique to a particular manufacturer or a vehicle from that manufacturer.

While this system of identification eliminates most of the confusion surrounding DTC definitions, it also multiplies the number of available DTCs for a particular vehicle by several fold. We checked the power-train DTC list for a late model Subaru Legacy and found there were over 100 possibilities. There’s no way you’re going to be able to memorize all those DTCs, so reliable service information becomes even more important than it has been in the past.