2 Chronicles 22:3

He also walked in the ways of the house of Ahab: for his mother was his counsellor to do wickedly.

He walked in the ways of the house of Ahab by following its evil, wicked, and idolatrous practices. His mother Athaliah was his counselor to do wickedly, advising him to do wickedly and leading him by her influence to do evil in the sight of the Lord. Under her influence and the counsel of that family he was guided into evil.

He aligned himself with his relatives in the house of Ahab, including his uncle Jehoram of Israel. That alliance with his relatives helped lead him into apostasy. After his father's death he followed that family's counsel, and it led to his destruction.