Though his election had been valid, he was invested by Conrad II, but the papal legate declared him a simoniac and deposed him.
Arnulf went into a brief retirement of penance at the Abbey of San Pietro al Monte at Civate, where Anselm III had gone for a similar reason during his episcopate.
It was performed by three great bishops of the German Gregorian Reform: Thimo of Salzburg, Odalric of Passau, and Gebhard III of Constance.
Only two of Arnulf's acts as bishop survive and he is buried in the Abbey of San Pietro al Monte at Civate.
His exile or burial there probably prompted a burst of artistic activity, with frescos and sculptures that remain unusually intact.