§1. The diocesan bishop is to appoint a coadjutor bishop and the auxiliary bishop mentioned in can. 403, §2 as vicar general. Moreover, the diocesan bishop is to entrust to him before others those things which by law require a special mandate.
§2. Unless the apostolic letter has provided otherwise and without prejudice to the provision of §1, a diocesan bishop is to appoint his auxiliary or auxiliaries as vicars general or at least as episcopal vicars, dependent only on his authority or that of the coadjutor bishop or auxiliary bishop mentioned in can. 403, §2.
Source: Code of Canon Law (Vatican.va)