Charles Ellicott Commentary 2 Kings 15:9

"And he did that which was evil in the sight of Jehovah, as his fathers had done: he departed not from the sins of Jeroboam the son of Nebat, wherewith he made Israel to sin." — 2 Kings 15:9 (ASV)

As his fathers — that is, the dynasty of Jehu, of which he was the last member. Like all his predecessors, he upheld the illicit worship established by Jeroboam I.