Problem With Navigator Air Suspension

These codes must be cleared or the "Check Suspension" warning message will be turned on.

• All service modules are built with the C1990 code. All assembly plant modules are built with the C1991 code. These codes can only be cleared using the following procedures.
• C1990 and C1991 can be re-enabled in the control module by resetting the ride heights to their default value, or when the pneumatic test has failed. When either one of these DTC's are present, the air suspension warning will be enabled.

Clearing C1990 or C1991

1. Either start the vehicle or put vehicle on a battery charger to ensure sufficient battery voltage.
2. Vent the vehicle down to the kneel position. (Having the key off, transmission in park, air suspension switch on and all openings, doors and liftgate glass closed will make the vehicle kneel.)

    

   NOTE:DO NOT SIT IN THE VEHICLE DURING THIS PROCESS. THE VEHICLE MAY NOT KNEEL OR MAY KNEEL VERY LITTLE IF THE HEIGHT OF THE VEHICLE IS NEAR THE KNEEL POSITION.

    

    

3. Pump the vehicle to the current calibrated trim height by turning the key to run, shifting to drive, and then returning to park and closing all vehicle openings (message center should show no openings ajar). Vehicle will then pump to the currently calibrated trim height.
4. Connect the NGS or WDS to the vehicle (make sure that the UBP cable is used if the NGS is the tool being utilized).
5. Using the NGS Service Card (green card) software version 11.2 or later, or WDS software version B25 or later, command the pneumatic test.
6. Run the pneumatic test. Due to vehicle network issues, the NGS may drop out before the test completes. When this occurs, rerun the pneumatic test with no one in or on the vehicle. If the test has been running for 5 minutes or more, the NGS has dropped out. The tester will indicate if the vehicle has passed the test.

    

   NOTE:PASSAGE OF THE PNEUMATIC TEST DOES NOT ELIMINATE THE POSSIBILITY OF MALFUNCTIONING SOLENOID VALVES.

    

    

7. After passage of the pneumatic test, use NGS Diagnostic Card (redcard) version 22 or later (or WDS Software version B25 or later) to retrieve any DTCs. If C1990 or C1991 is present, go to Step 8 and calibrate the ride heights. Otherwise, go to Step 10.
8. Using the NGS Service Card (green card) software version 11.2 or later, or WDS software version B25 or later, manually raise and lower the vehicle to the correct ride height as defined in Workshop Manual Section 204-05 on an alignment machine and calibrate the ride heights.

    

   NOTE:MANUAL SEND MODE ON THE NGS WORKS BETTER THAN THE AUTO SEND MODE. (NOT APPLICABLE TO NGS GREEN CARD 11.2.)

    

    

9. Using the NGS Diagnostic Card (red card) version 22 or later, retrieve the DTCs and verify that all DTCs have been cleared.
10. Drive vehicle and verify the repair. Verify the "Check Suspension" message is gone. Make the system vent to kneel and pump to trim several times while verifying system function.

source: http://www.ford-trucks.com/tsb/tsb.php/m-LINCOLN/d-NAVIGATOR/y-2003/t-03132

source: http://www.justanswer.com/ford/1b8w7-suspenion-having-problems.html <---This article should be read in its entirety. Its all about the issue you are having.