Joash of Judah reigned forty years 2 Kings 12:1, and Joash of Israel ascended the throne in his namesake’s thirty-seventh year 2 Kings 13:10; hence, we should have expected to hear that Amaziah succeeded his father in the fourth rather than in the second year of Joash (of Israel). The usual explanation of the discrepancy is to suppose a double accession of the Israelite Joash - as co-partner with his father in the thirty-seventh year of his namesake, as sole king two years afterward.
Related Commentaries of 2 Kings 14:2
2 Kings 14:2
2 He was twenty and five years old when he began to reign, and reigned twenty and nine years in Jerusalem. And his mother's name was Jehoaddan of Jerusalem.