A camshaft phaser control system including a camshaft target wheel, the target wheel having first and second teeth for measuring camshaft oscillatory instability. The trailing edge of the first tooth coincides with the negative camshaft oscillation peak, and the trailing edge of the second tooth coincides with the positive camshaft oscillation peak. During each camshaft rotation, each tooth initiates an input signal to generate first and second input signals in known fashion. During crankshaft rotation, a third input signal is generated corresponding to the rotational position of the crankshaft. From these signals, operational camshaft oscillatory instability is computed by an engine monitoring system (EMS). Any deviation from the operational instability while the engine is operating is a direct measurement of oscillatory instability of the camshaft about its nominal holding position. A change in oscillatory instability is inferred as system malfunction, permitting defensive action to be taken by the EMS.