Methods for diagnosing a fault of an oil piston cooling jets valve of an internal combustion engine are provided. A method includes sensing a pressure value in a main oil gallery and checking whether the oil piston cooling jets valve is commanded in a state for opening a communication between the main oil gallery and an auxiliary oil gallery or in a state for closing the communication. A pressure value in the auxiliary oil gallery is checked to as to whether it exceeds a predetermined threshold value thereof, above which a jet nozzle of the auxiliary oil gallery automatically opens. A fault of the valve is identified if the pressure value in the main oil gallery exceeds the predetermined threshold value by a predetermined quantity and if a pressure value in the auxiliary oil gallery is different than expected on a basis of the state of the valve.