Purrm3, yes that is correct.
Indeed, the liver enzyme CYP2D6 is responsible for the metabolism of hydrocodone, codeine, and dihydrocodeine to their active metabolites; hydromorphone, morphine, and dihydromorphine.
If a metabolite is "active" it too occupies an opioid receptor and helps reduce pain.
All of these active metabolites occur in fractions, some less than 10% of the total amount of hydrocodone.