We only publish a code once we have a genuine, original explanation for it in this language — not a placeholder or a machine translation. Coverage is expanding over time; if a code you're looking for isn't here yet, try the lookup tool, which may have it in another language.
Generic codes (the second character is 0, e.g. P0420) mean the same thing on every car regardless of make. Manufacturer-specific codes (second character 1, 2 or 3) are defined differently by each brand and aren't covered here yet.