Air Suspension Troubleshooting

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Staff member
Sep 12, 2023
North Ridgeville, OH
Vehicle Details
1997 Thunderbird 4.6, 1998 Mark VIII LSC
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One end of the car falls to the ground
This is indicative of a leak on the falling end of the vehicle. A sudden drop while driving is typically a catastrophic failure (blow out) and rare unless something happened like hitting a curb, pothole, or other car.

You may also experience a sudden drop while driving over rough roads, or when you flex the suspension a great deal at speed. This is because the cracks/leaks in the bags have been exposed when the air spring is compressed beyond the normal height.

Typically the air spring deflates over time (while parked at work, overnight, etc.) This is a slow leak that should be fixed promptly. Failing to fix the leaking bag will result in your compressor running excessively to keep the air bag(s) inflated, and will cause it to overheat and fail prematurely. See the section below on a detailed leak test procedure.

You get a check suspension light but the air bags are not deflated, or you get a check suspension light at speed on the freeway.
This is because air can’t get out. The system adds air to compensate for loads and to lift the car to driving height. When it wants to remove air (load removed, lower ride height on highway), it vents. The vent solenoid valve on the compressor frequently rusts closed due to moisture in the system (THIS IS WHY YOU MUST FIX LEAKS PROMPTLY) caused by leaking bags or atmospheric conditions. The air compressor is located in a tray in the right front fender of the car. You can remove/replace it by either removing the bumper cover and working in front of the tire, or you can remove it by removing the splash shield and working in with the tire.

This can also be caused by stuck vent solenoids at the air bags. These can be tested by removing them and applying 12 volts to the contacts. An audible click should be noted when applying and removing voltage - the absence of this indicates a faulty vent solenoid.

Check air ride light 90 seconds after key on.
The compressor will turn off after 90 seconds of continuous operation to prevent overheating. It will not run any longer as a fail safe. This is usually indicative of a leak in the system, but could also be a worn out compressor that is not creating enough pressure to inflate the air bags. To search for leaks, use soapy water on all the air line connections (one at each wheel, four in the compressor) while the compressor is running. This is usually also accompanied by lower than normal ride heights or recent system service.

Check suspension light comes on immediately with key on; compressor does not run.
This is usually a power/electrical issue. Quickly rule out the compressor relay by swapping it with the ABS relay, found in the driver's fender. If this solves the problem, you need a new relay. Also check the fuse. The compressor can function while increasingly drawing more and more power to overcome imminent internal failure, until it reaches the fuse limit. When that happens, you need a new compressor.

How can I test the Air Ride Function?
You can run an automated test sequence on the air ride system. If the testing hits a fault, it just stops at that point. The operator monitoring the KNOWN testing sequence is what identifies the fault.

Hold the suspension test connector with the open end of the plug facing you. The top row of terminals (from left to right) are pins 1, 2, 3, 4. The bottom row are 5 and 6.
The wire color for pin 2 is W/LB. Turn the key on, close the door, connect the test light from pin 2 to battery ground, and let the fun begin!

You can also use an OBD-I test scanner:

1. Turn ignition on​
2. Unplug test plug (found near the air cleaner box)​
3. Plug in reader​
4. Flip switch to TEST​
5. Tests run automatically​

Here is the order of testing:
  1. LF solenoid clicked open/close
  2. RF solenoid clicked open/close
  3. Rear solenoids clicked open/close
  4. Compressor vent valve clicks
  5. Compressor runs for a few seconds then shuts off

Then the system does a height sensor test:
  1. Compressor turns on, front valves open, and the front of car should rise. Front valves will click closed, rear valves will click open then the same thing happens for the rear.
  2. Compressor turns off and all valves are closed.
  3. Front solenoids clicked & front lowers
  4. Rear solenoids clicked & rear lowers

If you have access to the Rotunda Super Star II OBD-I tester, you can perform pinpoint air suspension diagnostics. See the section below for details on this process as well as how to retrieve air suspension trouble codes to aid in your diagnostics.
from American Air Suspension​

The Ford shop manual recommends using a soapy water solution for air suspension leak testing. While this is the absolute sure-fire way to leak test, if you don't have the right equipment and/or experience, the results of your test may not be conclusive. The equipment I'm speaking of is not the soapy water solution, but more the vehicle lifting equipment needed to allow you to get under the car and see most of the air spring...."WHILE THE WEIGHT OF THE CAR IS ON THE AIR SPRINGS". An example of this would be a front end rack - the kind of rack that is used to align a vehicle and that the technician has to drive the car up onto. If the rear of the car is on the ground, you can't safely get under it to visibly see all around the air spring. Using a front end rack, you can lift the vehicle up in the air and safely see the entire rubber bladder while performing the test. The problem is, most novice mechanics don't have access to a front end rack. With that being said, here is a much easier and safer approach to leak testing. I will explain this later on, but first let's explain a few things.

First of all, the rubber used on the air spring gets dry rotted mostly on the fold of the rubber, or where the rubber folds around on the bottom. This folded area of the rubber gets the blunt of the punishment and dry rots at a much faster rate than the rest of the rubber. Because this area dry rots faster than the rest, this is where your leak is going to be 99.9% of the time.

The reason the air spring will leak some times and not others, has a lot to do with temperature and most importantly, where the fold of the rubber is. The area of the rubber that's on the fold will change with vehicle height. In other words, the fold of the rubber will be in a different area while the car is being driven (city height) as opposed to when it is sitting still (vented/highway or parked height). If the dry rotted area of the rubber is "on the fold", this will open up any cracks in the rubber and allow air to escape.

Keep in mind that ALL the air springs have their own vent solenoid. The solenoid acts as a gate for air. No air should go in or out unless the solenoid is opened up by the control module. By turning the suspension switch off, you're disabling the solenoids, thus no air should escape... unless of course, there's a leak.


By far, the easiest way to test for a leak is to allow the car to vent down after shutting off the engine and opening and closing the door.


If nothing else, wait 5 minutes after you turn the ignition off, then turn the suspension switch off. The car should have vented by then.

After this, turn the suspension switch off and measure the height of the 4 corners of the car with a tape measure and write it down.

Now drive the vehicle for a few days, or until there's a noticeable difference in ride height. Don't try to drive the car if the car is noticeably low!

If the vehicle has a leak, the car will have gone down after driving.

NOTE: Depending on the severity of the leak, it may take more than one day to leak down. This is the case more times than you would think.

By all means, if the car goes down after 10 minutes of driving, turn the switch back on and resume your journey. You have answered your question.

Could it just be a leaky solenoid?

Most of the time, if the solenoid has never been removed before, most likely the leak isn't from the o-rings that seal the solenoid to the air spring. If the solenoid had EVER been removed before, the o-rings should have been replaced at that time. If you have an old o-ring that has never seen the light of day and all of the sudden, after 10 years of being cooped up, it is released from tension, it will expand. If reused, it WILL eventually cause a leak. It might take a day, a month, or even a year, but it WILL leak at some point down the road.

In other words, if you replace your air springs, make sure you replace the 2x o-rings that seal the solenoid to the air spring. If you don't, it's not a matter of "IF" it will leak, but more like "WHEN". It would be in your best interest to also replace the little o-ring that seals the air line to the solenoid at the same time. Since this o-ring is AFTER the actual sealing part of the solenoid, if this o-ring leaks, it will only affect the operation of the system while the solenoid is opened, like when the module is making a height adjustment - not while sitting overnight.
Retrieving and Clearing DTCs on the Lincoln Mark VIII
Using a Rotunda Super Star II Tester

From American Air Suspension

Before trying to retrieve any codes in the system, you may want to have the battery and charging system checked. A weak battery will cause all sorts of problems in the air suspension system. AutoZone and a few other auto parts stores will usually do this for free.
Function Test Procedure

Note: Run test 211 before running any tests. This will display any trouble codes stored in memory.
  1. Open hood and locate diagnostic connector on front of RH front shock tower (This connector is on the pass. side shock tower and will usually have a black cap reading "SUSP/EVO").
  2. Install battery charger to provide power during testing.
    NOTE: If you have a bad battery (weak cell), you may still experience problems during this test even though you have the battery charger on the vehicle.
  3. Open luggage compartment and ensure air suspension switch is OFF.
  4. Set Super Star II Tester mode switch to FAST and set selector switch to EEC/MCU.
  5. Turn Scan Tool power switch on.
  6. Set HOLD/TEST push button in HOLD position (Button is up)
  7. Turn ignition switch to OFF, then ON.
  8. Ensure both doors on vehicle are closed (the system most likely will not do ANYTHING while the doors are open).
  9. Install Super Star II Tester in diagnostic connector
  10. Press HOLD/TEST button and latch in TEST position (button is down).

    Codes for function tests will be displayed one after the other, cycling every few seconds through each item on the list.
    When the desired test code number appears, release the HOLD/TEST button to hold on the desired test, then depress it when you are ready to run the test. The selected action/test will run until you release the HOLD/TEST button again. Press the HOLD/TEST button to resume cycling through the tests on the display.

    This is an excellent way to test independent parts of the system and/or perform wiggle tests (this is to power up a part, then "wiggle" the connector in order to find a loose connection and/or bad wire). It is also the easiest way to test a ride height sensor, by listening for the beep. The closer the beeps are to each other, the closer to trim height you will be. If you don't hear the beeps, or you heard a beep, then it quits, you know you have a bad sensor.
Test code/description

211Display Code(s) in memory
212LF corner pump, with audible sensor check
213LF corner vent, with audible sensor check
214RF corner pump, with audible sensor check
215RF corner vent, with audible sensor check
216LR corner pump, with audible sensor check
217LR corner vent, with audible sensor check
218RR corner pump, with audible sensor check
219RR corner vent, with audible sensor check
221Compressor Run
222EVO actuator output test (toggles all solenoids and actuator)
223LF corner height sensor trim detection, with audible feedback
224RF corner height sensor trim detection, with audible feedback
225Rear height sensor trim detection, with audible feedback
226Speed sensor detection
227Pulse EVO actuator
228Clear all codes

Unlatch HOLD/TEST button to end selected test and to continue scrolling through the other codes. Relatch button to re-enter code display function.

Suspension trouble codes and possible cause(s)

15No faults stored in memorySome problems don't set a code
18Module detects low batteryBad battery and/or malfunctioning voltage regulator
19Module detects high batteryBad battery and/or malfunctioning voltage regulator
20Module memory errorBad module
25Height sensor power not 5 VoltsMay be a bad sensor or a wiring fault
35EVO actuatorEVO sensor disconnected or a wiring fault
45Steering sensorSensor disconnected or a wiring fault
50LF height sensor out of rangeMay be a bad sensor or a wiring fault
55RF height sensor out of rangeMay be a bad sensor or a wiring fault
60Rear height sensor out of rangeMay be a bad sensor or a wiring fault
70Vent solenoidMay be a bad compressor vent solenoid or a wiring fault
75Compressor relay control circuitMay be a bad relay or a wiring fault
80LF solenoid circuitMay be a bad solenoid or a wiring fault
85RF solenoid circuitMay be a bad solenoid or a wiring fault
90LR solenoid circuitMay be a bad solenoid or a wiring fault
95RR solenoid circuitMay be a bad solenoid or a wiring fault
98Compressor run time exceededAir leaks or weak compressor - compressor 90 second runtime limit reached
99Unable to detect raising or loweringClogged dryer or bad vent solenoid(s)
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