An air pressure differential sensing system includes a conduit defining an air passage through which air flows upon application of an air pressure differential across different regions of the air passage, a flap pivotally connected to the conduit, and a sensing device mounted proximate to the air passage and separate from the flap. An operating parameter is selectively written to or read from one of the registers for storage of an operating parameter as a function of a first or second state of a configuration signal that is applied to an address connection. For quick and easy temporary fixation and final fixation, in which no additional securing aids are required, it is proposed that the fastening device is configured as a snap connection with a temporary fixation and a final fixation and makes a single piece with the vehicle cowling part andor the add-on part.