Air leak.
Switch? Relay?
i"m not sure if a Lincoln navigator would have a sway bar, But my sway bar broke in my Chevy celebrity once and the whole car would rock side to side after turns and such. it's a bar by the rear axle and mine literally broke in two.
Trouble code P0401 means: Exhaust Gas Recirculation Malfunction
The Ignition Coil is the one that cause misfire or Spark Plugs
Bring to a shop that has an ABS scanner to determine the problem
On a 2003 Lincoln Navigator : A problem has been detected with the Anti-lock Brake System It could be a fuse , a sensor , or some other problem As long as the red " BRAKE " light is not on in your dash , you still have " normal " brakes
A headlight leveling system adjusts the vertical aim of the headlights based on the position of the rear suspension. As you load the trunk of a car, bed of a truck, etc. the suspension is compressed to allow the vehicle to ride smoothly. This causes traditional headlights to aim higher. A headlight leveling system lowers the headlight beam to compensate for this allowing the driver to see the road clearly without blinding oncoming traffic.
there can be many different problems but it could be a bad relay switch to check it get on the floor on the passenger side and check to see if the air suspension relay switch is on, try that for now, usually if someone uses a jack to raise the car and the tires have to come off the ground,they switch it off, so the height sensors don't mess up. but it this causes the check suspension light to come on.
Something is wrong with your air suspension.
A bobbing noise in front of a 2004 Lincoln Navigator could be caused by several issues, such as worn or damaged suspension components like struts or shocks, which may lead to excessive movement and noise. Additionally, loose or damaged sway bar links or bushings can produce a clunking sound during bumps. Another possibility is a problem with the tires, such as uneven wear or a defect that causes them to bounce. It’s advisable to have the vehicle inspected by a mechanic to accurately diagnose the source of the noise.
A problem has been detected with the Supplemental Restraint System ( air bags for front passenger and driver ) Take it to a professional