Abstract: A camshaft phaser includes an input member; an output member defining an advance chamber and a retard chamber with the input member; a supply passage; a vent passage; and a valve spool within the output member which is moveable between a first and second position. The first position prevents communication between the advance chamber and the vent passage, prevents communication between the retard chamber and the vent passage, and allows oil to flow from one of the advance chamber and the retard chamber to the other of the advance chamber and the retard chamber. The second position provides communication between the vent passage and one of the advance chamber and the retard chamber, prevents communication between the vent passage and the other of the advance chamber and the retard chamber, and provides communication between the supply passage and the other of the advance chamber and the retard chamber.