The Lincoln Navigator (which is just a Ford Expedition with a different grill) is a luxury Sports Utility Vehicle (SUV) sold by Ford that uses an innovative four corner leveling system to ensure the SUV has a comfortable ride over the bumpiest of roads. It accomplishes this feat through the use of air suspension, using air bags instead of normal springs. These air bags can be selectively inflated or deflated to give a better ride. However, this air suspension setup is considerably more complex than a normal spring suspension so troubleshooting is often necessary.
Look at the Lincoln Navigator from the outside. Note if any corner of the SUV is riding lower than the others. If only certain corners are having a problem, then the issue may be localized to that wheel well. Each wheel has its own airbag, height sensor and air line. If any one of those components is damaged, that wheel well will ride lower. If all the corners are riding low then a core component like the pump or tank could be damaged, or worse, all the individual wheel well components have gone bad.
Turn the Lincoln Navigator on and listen for the air pump to engage. The air bags will leak naturally over time when the car is off. The air pump engages when the SUV is turned on to refill the tank, and then the air bags. The pump will sound like a far off whirring fan. If there is no whirring, either the pump is damaged or all the height sensors in each wheel well are damaged. If there is whirring but still no air going into any of the airbags, the tank may have a hole in it, the air manifold may be broken, or the air lines may be broken.
Wait 15 minutes to allow the pump to try to fully inflate the air bags. Make sure the SUV is in "Park" and the emergency brake is on before you get out. Walk around the Lincoln and observe the corners. If one corner is dropping then the height sensor is broken or there is a tear in the air bag. If there is a tear in the air bag you should hear the air leaking out of the bag. If there is no leaking sound then the sensor is broken.
