A system includes a base having a sensor opening. An object-detection sensor is aligned with the sensor opening. A motor and a guide are each supported by the base and are spaced from each other. A continuous band is flexible relative to and engaged with the motor and the guide. At least a portion of the continuous band is transparent and extends between the sensor and the sensor opening. If a contaminant, e.g., dirt, water, snow, etc., is on the continuous band at the sensor opening, the motor moves the continuous band to locate a clean section of the continuous band at the opening.