Ethics codes by themselves cannot build true business ethics any more than laws can build law-abiding citizens. Ethics codes can only provide people with a nudge towards acting in truly ethical ways.
True business ethics come from within the business person. They are caused by a person’s value system. When a person has true business ethics, they will not commit unethical acts even if there is no chance that they would be caught doing so. They will behave in an ethical way because they feel that it is important to behave in such a way.
A code of ethics that a firm sets up cannot cause a person to have the values necessary to be truly ethical. Instead, all they can do is to try to rein in those who are not ethical. In the best of cases, these codes can help to build ethics. They can hold a person back and give that person enough time to develop an ethical sense of their own. But the code cannot create the ethical sense. It can only give the person the opportunity to develop that sense of their own accord.