03 lincoln navigator air suspension

You need to check your real axle sensor it may have come loose or broken

One of the easiest ways to check for leaking air struts, springs, or solenoids is to shut off the air suspension via the air suspension switch, which is often located either in the trunk or on the right side of the passenger foot well, and leave the vehicle sitting overnight. If you find your Expedition or Navigator has lowered a few inches or more, your probably have a leak somewhere in your air suspension. Hunting it down is as simple as letting your vehicle raise to its factory height, and spraying down your air struts, springs and lines with soapy water. If you notice any consistent bubbling from any component, you can be sure you have sprung a leak. Best of luck.

Sounds like everything's starting to go. These Navigators were FAMOUS for their poor quality air suspension. A lot of people are deciding to just ditch the air suspension altogether and just switch to standard coils. You can buy a kit like this one to do that. Really inexpensive and will last you at least through the life of the car.
2003 2006 Lincoln Navigator 4 Wheel Standard Air Suspension Conversion Kit...