Diagnostic of hydraulically switchable engine mechanisms

A method for detecting failure modes of latching mechanisms in a hydraulically switchable variable valve activation system of an internal combustion engine includes the steps of: integrating a pressure sensor in an engine control system including a plurality of switchable mechanisms connected to a common hydraulic gallery, an oil control valve downstream of the oil gallery, and en engine controller activating the oil control valve and the pressure sensor; measuring fluid pressure of the gallery with the pressure sensor; and determining if a failure mode of latching mechanisms occurred by evaluating the measured fluid pressure. Sudden flow changes that produce high frequency fluid pressure oscillations in the oil gallery are detected with the pressure sensor and evaluated by an engine controller to detect lock pin failure modes, such as lock pin ejections and operation of two-step RFF in a low lift mode at elevated engine speeds.