Air suspension issues? Maybe I can help. '00 Navigator BIG READ!


This info is for 98-02 Lincoln Navigator 5.4 V8 4x4 Four wheel air system!!! But it's still usable for the two wheel air system as it's basically half of these parts.

These cars are very uncommon where i live, as I'm from Hungary. Nonetheless i came upon one with back of the car on the ground, and was promptly tasked with fixing it.
I hope i can help someone with the info i can provide in this post. Beacuse i couldn't find anything comprehensible on the subject.

Firstly, there will not be any need for tools like an OBD scanner. Just a regular Digital MultiMeter, a simple testlight, test cables and some handtools. And you should hook up a battery charger, beacuse testing will deplete the battery very fast.

Step one:
!!!Verify the complaint.!!!
The Air suspension needs the following intput and criteria to start the leveling process.
-Door Ajar sensor - All doors closed, even the tailgate glass.
Mainly the Drivers door. Check the light for it in the dash, it should go out when you close the door. Also the cabin lights and the small lights outside on the step.
- Transmission in PARK.
- Handbrake not in use.
- Brake pedal, and Accelerator not pressed.
- Key in the RUN position.

If these are met, then the car should start leveling itself. If it's low, it'll start up the compressor and open the necessary valves to pump up the airbags. If it's high, it'll just vent to atmosphere.

If it doesn't do any of that, then you're in for a treat. :mad:

Step Two:
Check the components of the system.
It should be in the on position, but you never know...

-Air bags/shocks
Inspect the bags in the back visually, or spray them with soapy water and check for leaks. Same on the front shocks. The 4WAS system uses the front shocks for damping only, as the ride height is mainly handled by the torsion bars. Spray them very thoroughly fromt top to bottom. If there isn't any air in the system(But everything else works!) fill it up by manually running the compressor - explained in the Air Compressor paragraph - and check for leaks that way.

-All the fuses
There are 3 in the cabin fuse box and one in the engine bay fuse box.
The cabin ones are Fuse 4(15A), Fuse 6(5A), Fuse 20(5A). The engine bay one is Fuse 109(50A) which is hot at all times.

- Air Compressor (Never run it for more than 1-2 minutes! It'll melt under extended runtimes.)
The compressor is located in the engine bay on the passenger side under the washer fluid reservoir. Three bolts hold the jug in place sized 13mm. Move the jug aside, and you shold see the compressor assembly. Find the connector for compressor power, should be attached to the wheeltub. Pull it apart and put two test wires on the battery posts, and test the compressor by clpiing the testwires to the big gauge wires in the connector(polarity doesn't matter). That should run the compressor, but never run it for more than 10-15 seconds like this. Give it a listen, if it sounds like any other compressor, it's probably fine. If it doesn't budge, then "There's your problem lady!". Replace the faulty part, then do Step one again.

- Compressor Relay, or as it is called here the Air Suspension Module (The parts guy ordered me the wrong part beacuse of this!)
It is located on the passenger side, in a small nook right between the bumper and the wheelwell. Check the connector for corrosion or snapped wires. You don't need to take the relay out to test it. There are four wires going to it. The two big ones are the compressor power wires, which are usually fine. You have to focus on the two small wires. The one on the edge of the connector (usually dark blue and yellow) is the signal or trigger wire. Comes straight from the Air Suspension/Steering Control Module. the other small wire is the ground. Backprobe the small wires while the connector is in place, and bridge them with a test wire or a testlight. If the relay is fine, it should turn on the compressor. If it's not running the compressor but the compressor itself is fine, then replace and repeat Step one.

- Both Ride Height Sensors (In the 2WAS there's only one in the back.)
Ont the 98-02 production run cars there are two of these. Both on the drivers side. One behind the front left wheel mounted on the upper control arm towards the cabin the back one is attached between the frame and the stabilizer bar. Detach the lower mount and check for unobstructed movement. It should have a travel of about 80mm, but if it's moving freely for the whole travel and not binding, then it's probably fine. These are 5 volt sensors, simple potentiometer circuit. Disconnect the connector and check for power (should be 5 volts, but can go up to 6.), on the front the tan wire is the signal wire while on the back it's the black/orange one (easily indentifiable by being the only odd wire). If power is getting to the sensor, you'll have to check the singal wires. Find a good ground on the chassis or use the ground wire of the sensor. Backprobe the signalwire, and actuate the sensor by hand. On your DMM you should see that the voltage goes from about 0.5 volts fully extended to 5.3 volts on full compression. 2.4-2.8 volts is the ideal for the suspension as that's the voltage you should see at optimal ride height. If the sensors don't show anything or are stuck on a specific voltage, but all other components work fine, then replace the parts at fault, then repeat Step one.

- Air Suspension/Steering Control Module (Same in both the 4WAS and 2WAS cars.)
It is located in the dash right above the radio. You can get to it by removing the top panel that goes from around the radio all the way to the driver's door. Remove the panel at the radio by turning the vents inward, grip it inside the frame that goes around the radio/HVAC unit and pull firmly. It should pop off as it is only held in by clips. Next you take off the part that goes around the steering column just under the instrument cluster. Pop out the headlight controls as there's a screw behind it you need to remove. Take out the three bolts that hold together the parts that cover the cluster and the top panel. You now can pull the panel facing you out enough that you can get to the screw in the top left corner of the top panel. As you go aruond the perimiter of the top panel watch for screws that are need to be removed, and on by one as you remove them pull gently on the panel. When you removed to top panel, at the top of the radio you should see a black box held in by two brackets. There's three screws that hold the two brackets, take out the back one first by removing the two small hex heads (7mm for me) and the two phillips head screws. On the front you need to remove only the small hex head screw. You should be able to set the module aside to get to the wires. With the key in the run position find the Dark Blue/Yellow in the gray connector. That is the relay control wire you saw the other end of at the compressor relay. As this wire goes directly to the relay and you have access to both, it doesn't hurt to check for continuity by backprobing the connectors at the module and the relay and using your DMM. If the wire integrity is good, check for signal. The module gives a 12v signal to the compressor. I still don't have any specifics on the signal timeout interval or the values it should produce over time, beacuse i don't have access to a known good unit. In my case this was the fault. You can test the relay from here too, by shorting the control wire to ground. And can also check the height sensor inputs in the black connector at the tan and black/orange wires. The black connector is the input connector, the gray connector is the output connector. The black one has the door ajar sensors in a single wire at pin 5 (No color code on this one sorry. As my unit had a repaired wire here with 3! different color coded wires, but was otherwise working properly.). I checked for continuity on these wires(You will need a lot of jumper wires or very long ones.). If the wires are snapped or corroded repair them then Step one again. If everything checks out you might just have a bad module at your hands, if you're able to procure one then replace it and Step one again.

My fix:
I was able to install a manual switch for running the compressor. The module does everything else perfectly, apart from turning on the compressor. I don't know why, as it has all the correct inputs but somehow bodges the compressor signal output. I wasn't able to read the parameters or reset the height values with a scanner, as nobody has a scanner that can read this module in this country. Anyway, i fixed it by splicing in a switch into the dark blue/yellow wire to short it straight to ground, and now i can run the compressor manually while the module does the leveling part.

And that's how far i pursued the issue. As the issue was fixed by installing a switch and replacing both height sensors and the relay. It is now working fine by running the engine, switching the air suspension main switch on, and turning the compressor on with the installed switch, and turning it off when the car is raised and you hear the tone change of the compressor when it's working againts closed valves. By turning the main switch off after leveling will prevent it from trying to level every time you cycle the key. The downside is that the CHKSUSP light will stay on when the main switch is off (Incredibly there's info on how to kill this light, but nothing else.)

And after the epilogue here comes the part where i tell you to do any of these at you own risk if you are not a mechanic.

Feel free to add any helping information on the subject. Make this thread the go to thread for the air suspension problems on these cars.

Or you can just call me an idiot.