Various embodiments include a method comprising: moving a piston toward TDC in successive pump cycles; during the movement, closing an inlet valve by applying current to an electromagnet; generating a pressure signal downstream of the outlet; applying a measurement current to the electromagnet when the inlet valve is closed; while the piston moves away from TDC, detecting an opening position at which an opening movement of the inlet valve begins on the basis of a predetermined change with respect to time of the measurement current; checking whether a value sequence of the ascertained opening positions over multiple pump cycles satisfies a predetermined discrepancy criterion with regard to the sensor signal; and if the discrepancy criterion is satisfied, generating a fault signal relating to the pressure sensor.