A data storage device is disclosed comprising a head actuated over a disk surface, wherein the head comprises a plurality of elements including a write assist element. A bias signal applied to the write assist element is controlled such that the write assist element is substantially unprotruded, and while the write element is substantially unprotruded, an air bearing resonant frequency (ABRF) of the head and disk surface is measured. The bias signal applied to the write assist element is controlled such that the write assist element protrudes toward the disk surface, and while the write assist element protrudes toward the disk surface, the head is excited at the measured ABRF and the head touching down onto the disk surface is detected.