OBD codes are OBD codes. No real need to convert them.
OBD-Codes OBD-II Trouble Codes - DTC Codes Car Repair
The only situation that can be a problem is when the manufacturer has specific hex or decimal codes, but in the case they are not tied to OBD standards, your OBD tool will not read and display them anyway.
The OBD standard supports "extended" or manufacturer specific codes as long as the manufacturer follows the OBD standards and format.
The main thing you have to be careful with on any code, OBD or other, is they are just clues and just because a sensor may be listed in the description, it does not mean the sensor is actually bad. Many times the opposite.
So if you have a code that states something like O2 sensor limit has been reached, this means the O2 sensor is working, but the fuel mixture is consistently too far in one direction.
There should be no real reason to try and convert a Pxxxx code backwards.