it's a 3 wire sensor so you got a 5v feed, an earth, and a signal wire so make sure you have the feed and earth and then move the probe from the 5v feed to the signal wire and then move the arm on the sensor, you should get a varying voltage as you move the arm up and down. if you don't then that sensor is u/s and will need replacing but do this for both sensors so you can be certain what one has gone, also check the pins in the plug and the sensor as they are known for leaking water in and corroding away.
a faulty sensor or corroded pins are the only issues i ever came across when diagnosing the levelling issue but if both sensors move and vary the voltage then your looking at a wiring issues between the sensor and the ecu for the levelling or a faulty ecu but i never came across that it was always a sensor.