Question about 1998 Ford Expedition

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Rear air bag suspension failure 1998 Ford EXP E.B. 2x2

Good Evening. I'm the original owner and have 135K miles on this sport ute. Today after shutting it off & exiting, I heard a very loud "hiss", almost like setting air brakes from what may have been the compressor itself & the rear is down on the shocks (low-rider like). Came home & did some reading on the Internet. I found and removed the relay, looked clean, did the tap trick a few times & reinstalled. Turned key to on & compressor activated but still won't fill the rear bags. Could the compressor be bad, the relay perhaps, or the rear suspension solenoid or lastly perhaps the one below the master cylinder-still can't find it yet. Thanks so much in advanced. Perplexed sends. I replaced my air suspension compresseor and both air bags but comp. won't kick in. Sent straight power to comp. and it kicked in.

Posted by dianehenryb on


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gerry bissi

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This will get you started. report back on progress and we'll go from there. There is a diagnostic test that will provide codes I think. I will look.

The system consists of unique rear air springs, air compressor, air lines, air spring solenoids, height sensor, air suspension control module, attachments and associated signals derived from both driver and road inputs. With these components and signals, the air suspension control module commands changes in vehicle height that are necessary for the load leveling features.
The load leveling feature rear air suspension (RAS) systems shall automatically make adjustments in vehicle height so that the vehicle is always at trim height and constant front-to-rear vehicle attitudes are maintained over the expected load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle's left and right sides for RAS system shall be restricted to what can be reliably achieved with one air suspension height sensor.
The system uses one air suspension height sensor, a steering sensor, generic electronic module (GEM) transfer case inputs, and other vehicle sensors to measure driver and road inputs. The system changes vehicle height using an air compressor, two air lines, and the use of an air spring with an air spring solenoid.
The air suspension system holds vehicle height when the rear hatch or any door is opened. The system stores rear vehicle height the moment any open door is detected. The system then maintains this height regardless of the addition or removal of a load. The system will return to its commanded height when all doors are closed and the vehicle speed exceeds 16 km/h (10 mph).
Air Suspension Switch
The air suspension switch is located behind the RH kick panel on a mounting bracket. The switch interrupts power to the air suspension control module.
The air suspension switch supplies a signal to the air suspension control module. Without the air suspension control module receiving this signal the load leveling system is inoperative and will not react when rear of the vehicle is raised or lowered. If the air suspension system is disabled by turning off air suspension switch, a "CHECK SUSP" will appear in the RH corner of the instrument cluster with the ignition in the run position.
Air Compressor
The RAS air compressor:

  • Is not interchangeable with four wheel air suspension (4WAS) compressor.
  • Consists of the compressor and vent solenoid; neither are replaceable as individual items.
  • Is mounted in the engine compartment between the washer fluid bottle and headlamp (RH front corner).
  • Is a single cylinder electric motor driven unit that provides pressurized air as required.
  • Is powered by a solid state relay, controlled by the air suspension control module.
  • Passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
  • Air drier has a single port and is not interchangeable with 4WAS compressor air drier.
  • Air drier may be replaced separately.
  • Incorporates a snorkle that may be replaced separately.
The vent solenoid:
  • Allows air to escape from the system during venting actions.
  • Is located in the air compressor cylinder head.
  • Has a 160 psi internal relief valve.
  • Shares a common electrical connector with the air compressor motor.
  • Is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
  • Has an O-ring seal that prevents air leakage past the valve tip.
  • Opens when the air suspension control module determines lowering is required.
  • Provides an escape route for pressurized air that opens when system pressures exceed safe operating levels.
  • Is replaced with the air compressor as a unit.
Air Spring
RAS vehicles use air springs in the rear. The air springs provide a varying spring rate proportional to the systems air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system air. Increasing air pressure (compressing) raises the rear of the vehicle while decreasing air pressure (venting) lowers the rear of the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the air suspension control module.
The air springs are mounted between the axle spring seats and the frame upper spring seats.
The two air springs replace the conventional rear coil springs.
Air Suspension Height Sensor
When the air suspension height sensor indicates that the rear of the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.
One air suspension height sensor is mounted on the vehicle. The air suspension height sensor sends a voltage signal to the air suspension control module. The output ranges from approximately 4.75 volts at minimum height (when the vehicle is low or in full jounce), to 0.25 volts at maximum height (when the vehicle is high or in full rebound). The air suspension height sensor has a useable range of 80 mm (3 in) compared to total suspension travel of 200-250 mm (8 to 10 in) at the wheel. Therefore, the air suspension height sensor is mounted to the suspension at a point where full rear suspension travel at the wheel is relative to 80 mm of travel at the air suspension height sensor. The air suspension height sensor is attached between the No. 5 frame crossmember (upper socket) and the panhard rod (lower socket). Replace the air suspension height sensor as a unit.
Compressor Relay
The compressor relay is energized by the air suspension control module to allow high current to flow from the battery to the compressor motor.
  • A solid state relay is used in the air suspension system for air compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the air suspension control module.
Air Suspension Control Module
NOTE: The 4WAS air suspension control module is used for the RAS system. The internal processor recognizes external circuitry to determine if it is installed in a 4WAS or a RAS equipped vehicle.
NOTE: The air suspension control module is calibrated with information from the air suspension height sensor. A new or exchanged air suspension control module requires a ride height adjustment calibration process to be performed.
The air suspension control module controls the air compressor motor (through a solid state relay), and the air spring solenoids. The air suspension control module also provides power to the air suspension height sensor. The air suspension control module controls vehicle height adjustments by monitoring the air suspension height sensor, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals, and the brake pedal position (BPP) switch. The air suspension control module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing of the vehicle and related components.
The air suspension control module is mounted in the passenger compartment inside the instrument panel above the radio and temperature controls.
The air suspension control module monitors and controls the air suspension system through a 32-pin two-way connector. The air suspension control module is keyed so that the air suspension control module cannot be plugged into an incorrect harness. There are two sides of the harness connection to the air suspension control module. Each is uniquely colored and keyed to prevent reversing the connections.
Solenoid Valve, Air Spring
Rear air bag suspension failure 1998 Ford EXP E.B. - swj~us~en~file=ani_caut.gif~gen~ref.gif WARNING: Never rotate an air spring solenoid valve to the release slot in the end cap fitting until all pressurized air has escaped from the spring to prevent damage or injury.
The air spring solenoid:
  • allows air to enter and exit the air spring during leveling operations.
  • is electrically operated and controlled by the air suspension control module.
Air Suspension Diagnostic Connector
The air suspension diagnostic connector is used to aid the technician in diagnosing the air suspension system. It is also used to vent the system of compressed air when air suspension system components need to be repaired or replaced. The air suspension diagnostic connector is located under steering column.

Posted on Jun 01, 2009

  • gerry bissi Jun 01, 2009

    Visual Inspection Chart



    • Restricted suspension movement
    • Excessive vehicle load
    • Cut, severed, crimped air line(s)
    • Unmounted height sensor
    • Damaged air spring(s)

    • Open fuses:

      • I/P fuse 6 (5A), and I/P fuse 20 (5A)
      • Fuse 4 (15A) and fuse 15 (50A) in power distribution box

    • Loose, corroded, or disconnected connectors
    • Air suspension switch is in the OFF position
    • Damaged solenoid valve(s)


    dealer has to this with NGS tester

    1. If the concern remains after the inspection, use NGS Tester connected to the data link connector (DLC) to retrieve continuous diagnostic trouble codes (DTCs) and to execute On-Demand Self-Test diagnostics for the air suspension control module.

      • If the On-Demand Self-Test is passed and no DTCs are retrieved, go to Symptom Chart to continue diagnostics.

      • If DTCs are retrieved, go to Air Suspension Control Module Diagnostic Trouble Code (DTC) Index in this section.

      • If the air suspension control module cannot be accessed by the NGS Tester, go to Pinpoint Test Q.

    On-Demand Self-Test

    Verify that the following conditions are met before performing the On-Demand Self-Test.

    • All doors, liftgate, and liftgate glass must be closed.
    • The transmission is in PARK.
    • The brake pedal position (BPP) switch is not pressed during the test and the parking brake is not set.
    • The accelerator pedal is not pressed during this test.

    1. Fulfill the pre-conditions.

    1. Install a battery charger for the On-Demand Self-Test to prevent battery drain.

    1. Run the air suspension On-Demand Self-Test.

    1. Record all listed DTCs.

    1. Retrieve stored DTCs.

    1. Troubleshoot any On-Demand Self-Test DTCs first.

    1. Retest and clear DTCs after repair.

    Air Suspension Control Module Diagnostic Trouble Code (DTC) Index




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Just buy the conversion kit. Had the same problem wasted a lot of money.

Posted on Jun 16, 2009



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Switch to regular coils and springs I have this problem and after taking to many mechanics they all agreed that this a very problematic system so just cancel it and get a regular suspension its aprox $350.00

Posted on Feb 11, 2011

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