When Mayor Bill de Blasio announced last month that he was elevating Cynthia Brann to become the city’s new correction commissioner, he cited her experience, saying that “she knew the job, she knew the system, she knew the people.”

She apparently was not as well-versed on city ethics rules.

On the day of her appointment, Ms. Brann violated those rules when she dispatched a subordinate to obtain a cashier’s check, drawn from his own bank account, so that she could pay a fine, according to a case disposition released on Tuesday by the Conflicts of Interest Board.

Even though Ms. Brann reimbursed the subordinate, the board ruled that her actions still ran afoul of the City Charter section that states that no public servant shall use his or her position to obtain personal gain or advantage.

Ms. Brann had already proved to be ethically challenged: The fine, for $6,000, had been issued for her improper use of her official city vehicle, which she drove to suburban shopping malls and Kennedy Airport.