§1. In order to foster the present and future good of the diocese as much as possible, a diocesan bishop, a coadjutor, and the auxiliary mentioned in can. 403, §2 are to consult one another on matters of major importance.
§2. In considering cases of major importance, especially of a pastoral character, a diocesan bishop is to wish to consult the auxiliary bishops before others.
§3. Since a coadjutor bishop and an auxiliary bishop are called to share in the solicitude of the diocesan bishop, they are to exercise their duties in such a way that they proceed in harmony with him in effort and intention.
Source: Code of Canon Law (Vatican.va)