Diagnostic systems for two-stage oil control valves

A diagnostic system comprises a first pressure monitoring module, a second pressure monitoring module and a failure detection module. The first pressure monitoring module determines pressures at low lift and high lift at pressures in a cam phaser when a first oil control valve (OCV) moves first valve stem in a low-lift state or a high lift state. The second pressure monitoring module determines pressures at low lift and high lift at pressures in the cam phaser, when a second OCV moving second valve tappets in the low lift state and the high lift state. The fault determination module diagnoses a fault in the first OCV and the second OCV based on the pressures at low lift and the pressures at high lift.