Under APA rules, ethics codes are treated as reports. If the author is the same as the publisher, the publisher may be omitted.
American Psychological Association. (2017). Ethical principles of psychologists and code of conduct (2002, amended effective June 1, 2010, and January 1, 2017). https://www.apa.org/ethics/code/
If you are quoting directly from an ethics code, for the in-text citation you would put the section (may also be called provision or standard) name in place of a page number so the reader can quickly identify its location.
For example:
"Multiple relationships that would not reasonably be expected to cause impairment or risk exploitation or harm are not unethical" (American Psychological Association, 2017, Standard 3.04).
Narrative citation: According to the American Psychological Association (2017, Standard 3.04), "Multiple relationships that would not reasonably be expected to cause impairment or risk exploitation or harm are not unethical."
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