DTC C1801: Vehicle Height Sensor: Description
WARNING: This page is about a different car, the 2013 Nissan Armada. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle height sensor operates on a 5 volt reference signal from the suspension control unit. The suspension control unit also provides ground to the height sensor. Depending on vehicle height, the height sensor signal should have between 0.2V and 4.8V.