A gas spring fastener driving tool, having a cylinder filled with compressed gas that forces a piston/driver through a driving stroke movement; a rotary-to-linear lifter, then moves the piston/driver back to its ready position, preparing the tool for another driving stroke. The driver has protrusions (teeth) along its edges to contact extending pins of the lifter member, for lifting the driver during a return stroke. The driver's movements are detected by position sensors, and the information provided by those position sensors is used to prevent the lifter from impacting against the driver in situations where the driver did not finish its driving stroke in a correct (“in specification”) position. The use of two position sensors allows a Dry Fire diagnostic test to determine if gas pressure in the gas storage chamber is too high, or has become too low.