A diagnostic system includes a first pressure monitoring module, a second pressure monitoring module, and a fault determination module. The first pressure monitoring module determines low-lift pressures and high-lift pressures in a cam phaser when a first oil control valve (OCV) moves first valve lifters to the low-lift state and the high-lift state, respectively. The second pressure monitoring module determines low-lift pressures and high-lift pressures in the cam phaser when a second OCV moves second valve lifters to the low-lift state and the high-lift state, respectively. The fault determination module diagnoses a fault in one of the first OCV and the second OCV based the low-lift pressures and the high-lift pressures.