An improved control and diagnostic algorithm for coordinating the operation and checking reliability of oil control valves for a vane-type camshaft phaser in an internal combustion engine. A first oil control valve governs the rotational position of the phaser rotor within the stator, and a second oil control valve controls the locking and unlocking of a locking pin operable between the rotor and the stator. The algorithm determines when a change is needed in the position of the locking pin, commands the rotor to a predetermined angular position to permit the position change to be carried out, determines whether the commanded change was carried out successfully, and reports instances wherein the commanded locking pin position change was unsuccessful.