In the gemara sanhedrin 80a, it discusses correcting one's father and what the acceptable method would be. It says when correcting him "bdivrei torah" and the method being "it is written such in the Torah".. This seems to imply that one can only correct ones father in the acceptable manner regarding a deoraisa that he may have transgressed, but one could not correct his father for transgressing a d'rabonon.
Is this correct or is divrei torah meant to include any mitzva even a drabonon?
The formula given for correcting one's father, the indirect way, is said even if he merely misquoted a Shemu'a. It seems that letting the father figure out himself that he erred is not a problem no matter what the error was. (By the way, the Or ha'Chaim writes that if the father has not yet done the Aveirah that the son may do whatever necessary to stop him.)