When discussing a code of morals, choose the noun ethics. You might call a politician who uses taxpayer money for wild parties a little "ethics-challenged."
Ethics can mean the study of morality — what's right and wrong. When discussing this branch of philosophy, treat the word as singular, despite the "-s": "Ethics is no longer widely taught." But in the sense of "moral correctness" or "a moral code," treat it as plural: "The ethics of capital punishment are complex." Don't confuse it with ethos, which means "the characteristic spirit of a culture." (Both words come from Greek ethos, "moral character.")