There's a couple (that I know of, anyway) of different ways CEL codes are stored; "historic" (problem no longer occurring)are stored differently from currently occurring malfunctions. The Subaru dealership "Select Monitor" presumably will pull all types, I don't know about generic OBDII readers. Anyway, make your first stop at Autozone, if you're US, and get the codes hopefully read for free. Some are pretty self explanatory, some not; you can always come back here and post for help.