Generic OBD2 Fault Codes.

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With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive cycles. A drive cycle means starting a cold engine and driving it long enough to reach operating temperature.
The trouble codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle manufacturers use the same common code list and the same 16-pin diagnostic connector. Thus, a P0302 misfire code on a Nissan means the same thing on a Honda, Toyota or Mercedes-Benz. But each vehicle manufacturer also has the freedom to add their own "enhanced" codes to provide even more detailed information about various faults.
Enhanced codes (P1 codes), which are special OEM codes for specific vehicle applications, provide additional information and often cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, air bag codes and other body and electrical codes.
The second character in an OBD II will be a zero if it is a generic code, or a "1" if it is a dealer enhanced code (specific to that particular vehicle application).
The third character in the code identifies the system where the fault occurred. Numbers 1 and 2 are for fuel or air metering problems, 3 is for ignition problems or engine misfire, 4 is for auxiliary emission controls, 5 relates to idle speed control problems, 6 is for computer or output circuit faults, and 7 and 8 relate to transmission problems.
TROUBLE CODES For a more detailed explanation of the longer code numbers.