§1. The obligations and rights of a parochial vicar, besides being defined in the canons of this chapter, diocesan statutes, and the letter of the diocesan bishop, are more specifically determined in the mandate of the pastor.
§2. Unless the letter of the diocesan bishop expressly provides otherwise, a parochial vicar is obliged to assist the pastor in the entire parochial ministry by reason of office, except for the application of the Mass for the people, and to substitute for the pastor if the situation arises according to the norm of law.
§3. A parochial vicar is to report to the pastor regularly concerning proposed and existing pastoral endeavors in such a way that the pastor and the vicar or vicars, through common efforts, are able to provide for the pastoral care of the parish for which they are together responsible.
Source: Code of Canon Law (Vatican.va)