Relief Valves
A Lincoln Town Car's air suspension uses a small, separate air compressor under the driver’s side left fenderwell, and air lines run to the air bags. On top of each air bag is a electrical valve that serves as a relief valve that allows air to be exhausted when activated. The valve senses the amount of air pressure within the air bag to keep both sides equal. These valves are operated via a leveling sensor that is attached to the body of the car and to the rear axle by a movable arm. When the rear of the car drops because of an increased load, the arm is pushed up, turning on the air compressor and filling the air bags to level the car. When the load is removed and the arm moves down, indicating that the back of the car has risen, the sensor opens the valve on the air bags and allows air to escape, lowering the car.
Air-Suspension Switch
If the back of the car is low, indicating that the air suspension is not working, and the air suspension light is on, check the fuse. If the fuse is all right, make sure the air-suspension switch in the trunk is on. This switch is used when the car is in for service. Always turn off the switch before lifting the car, because the sensor will think the car is rising and keep the air bag valves open, ruining the rear air suspension.
Switch Terminals
Turn the ignition key with the engine off, and listen for the compressor to come on while pushing down on the rear bumper. If it does not come on, test the switch terminals for power with a circuit tester. If one terminal has power and the other does not, replace the switch.
If there is power, turn the switch to the "Off" position, raise the vehicle and place it on jack stands in the rear. Inspect the leveling switch on the axle, making sure it is not bent and is connected. Use an ohmmeter for this test. Pull the electrical connector off the switch. Loosen the arm of the switch from the axle. Test the switch with the ohmmeter by checking across both terminals while slowly moving the arm. There should be no continuity with the arm down. As the arm is raised, there should be continuity. If not, replace the switch. If there was continuity, connect the arm and the electrical connector.
Check for Power
Put a floor jack under the axle and raise the axle so it is just beginning to lift the car off the jack stand. Turn on the ignition. Turn the air suspension switch to the "On" position. Use the circuit tester to check for power at the leveling switch. If there is power, turn the air-suspension switch to "Off" and lower the car.
Access the air compressor in the front, under the hood, and check the electrical connector for power. If there is power, check for a good ground. If both are good, replace the compressor. If the compressor works and the car does not rise in the back, replace the air bags.
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If all this checked ok, go through this conversation :-----
Expert :the first thing youneed to chek will be the rear heith sensor and make sure it has not popped loose.
Expert :I will post a diagram of its location. It will be number 7 in the diagram.
Expert :
See image :---
Customer :hi, what's a heith sensor?
Customer :Also, which number is XXX compressor?
Customer :I will go check on that heith sensor...
Expert :the rear heith sensor tells the air suspention module how high or low the rear end is. It just pops onto a ball socket on both ends.
Expert :the compressor is nuber 10
Customer :the car is so low in the rear I need to jack it up to get under it to look for that sensor - i'll be back...
Expert :Make sure to turn the air ride off
Expert :You do not want to jack the car up unless the air ride has been shut off, do yuo know where the shhut off switch is?
Customer :okay, I'm back - yes, I know where the shut off is - I found the heith sensor and it appears to be plugged in fine - I took one end off the sensor and moved the plunger up and down - I then started the car and turned the compressor on but nothing happened - I think the compressor is dead now - which fuse do I check? I have a multimeter and can check for power somewhere - I have no indications of a problem in the display readouts on the dash -
Expert :Let me lk up the wire diagram and the location for the fuses. Be right back asap.
Expert :Fuse 3 in the fuse box under the hood is the fuse for the air compressore.
Expert :Did you check the fuses? If you have the air ride turned off the compressor will not kick on.
Customer :I checked every fuse in the box under the hood - I even checked the diodes and reseated all the relays in the box - the compressor started running but it stops after less than a minute and the rear end does not come up any - the front end is fine - no sag, How can I prove it is the compressor not pumping enough - maybe it is bad - can I pull the compressor and run it?
Expert :There ae a few tests we can run on the system to see what is going on, but the best thing to do would be to pull the control valves out of the front air bags and see if the compressor will pump themback up first.
Expert :If the front does come back up, then we know better what area we need to be looking at to correct the rear.
Customer :OK, where are they and are they just plug in electrical connections?
Expert :I amsorry but this car does not have front air ride, it uses a regular spring over strut set up.
Expert:Can you locate item 2 in the diagrami posted, this is the control module for the air ride and we need to do some testing on the wires to and from it.
Customer :Yes, I have seen this module and wondered what it was -want me to open it up?
Expert:
number 12 is the pcm.
Customer :And , can I just have regular shocks put on the rear witrhout too much trouble and I'll be done with this air ride system.
Expert :You would have to get a spring convertion kit to remove the rear air springs.
Customer :okay- so you want me to open the pcm module?
Expert :No I need you to get to number 2 in the truck, this is the ride control module, the pcm does not have much control over the air ride.
Customer :cool, thanks for that info on the spring conversion...
Customer :number 2 in the trunk...ok
Customer :compared to dragging right now I would accept a less smooth ride - but maybe we can figurre out what I am dealing with today...now what am I going to check on this number 2 module?
Expert :The module is in a tray under the rear window self. Let me post a diagram of its specific location.
Customer :ok
Expert :See image below:--- 
Customer :Ok- got it - which module in the drawing is it and what do I check - I have pulled the tray down in the trunk and see all the modules
Expert :number 7 is the air ride control module.
Expert :here is a pin out for the plug to the module, you will need this as a guid to know what wire and pin I am asking you to take readings from.
ExpertSee image below :---
Customer :Got it - where do you want me to check and for what?
Expert :You will need a paper clip, with te paper clip yucan slide along side the wires and into the plug so the paper clip is touching the metal onectors inside the plug so you do not have to poke a hole in the wires.
Expert :you will need to tesat pins 1,36,37, 56,57, and 58 to see if they have 12 volts with the ignition switch in the run position, or with the engine running.
Customer :I understand - ok - next
Customer :got it - I can go check it now
Expert:ok
Customer :I get 12 volts on wires 1, 36, 37, 38
Expert :There willbe some differances as the diagram is for both front nd rear air ride as well as jsut rear.
Customer :I get 5vdc on 58, .2vdc on 57 and 1.4vdc on 3 when the compressor was running pin 3 went to 12vdc when the compressor was not running - I need to run these checks again to confirm - does this info help?
Customer :Do I check while the compressor is running? Switch is on but not running?
Expert :I believe you have the chart wrong. When you look at the pin out iposted this is looking at the plug from the module side, not the back side where the wirees are.
Customer :I will verify - but I believe I was reading it right - no numbering on the plug - that would be nice to have - I'll check where the empty holes are and should be able to match it up correctly - I'll be back
Expert :ok
Customer :you were right - I found pin put numbers on the plastic part of the connector - I found 12vdc on all the wires that exist -
Expert :That is much better.
Customer :the compressor does run but nothing happens to the rear level - are we ready to say the compressor is the problem yet?
Expert :not yet. Lets trick the system and see if w can get the rear to rise up.
Expert :what I need you to do is run a jumper from pin 35 to pin 36 to activate the comprsssor, and
Expert :Then when the compresor is on run a jumper from pins 37 to 52 and see if the rr will rise up.
Expert :sorry about that pin 37 to pin 38
Expert :You can have the module unpluged to do this test if you woudl like.
Customer :I'll go try this now -
Expert :ok
Expert :you may have to run the jumper to pin 52 as well as pin 38
Customer :ok, when I jumper 35-36 nothing happens - I have the module still connected - nothing happened when I jumpered 37-38 but I just where I might have to jumper 52 as well as 38 so I'll try that - taking a lunch break -get back after that.
Customer :ty
Customer :ok--tried again, still nothing happens when I jumper 35-36 but I notice that if I have 37-28-52 jumpered the compressor only runs for a few seconds and stops - but when not jumpered the compressor will run for a minute or so but still no lift in the rear-
Customer :I have the module still plugged in when doing this- maybe I should try it with the module unplugged?
Expert :yes please try this with the module unplugged.
Customer :ok will do - back in a bit
Expert :ok
Customer :I jumpered all the wires like you asked- 35 to 36 and 37-38-52 all jumpered together. Is ther anything else I try - the compressor does run but the rear has collapsed all the way down - I have no suspension in the rear - can I tap into the air line somewhere to prove the compressor is actually pumping air?
Expert :You would have to pull one of the lines loose from the rear air springs, then trip the compressor on, and see if you get any pressure at the end of the line.
Expert :if you look on the air compressor itself, see if there is an air port like you woudl find on your tires. If there is one we may be able to get the rear to come up, with out the compressor, but you woudl need an air compressor for air tools, or an air tank.
Customer :I will look for a air port and I have a small compressor - either way - I'll check
Customer :what did my checks prove when I jumpered the wires? Nothing happened - does that indicate anything
Customer :hi - what should have happened when I jumpered the wires? What does it mean if nothing happened when I jumpered them?
Expert :When you run the jumpers, the right tear air bag shoudl have built up pressure and raised back up. With it not raising, then you either have a short to the air valve at the air spring, or the compressor is not buildingup any pressure as it is running.
More then likely the compressor itself is bad. It should have aired the one air bag up when you jumped out the plug and told the valves and compressor to let air in.
Expert :You may be bale to get a good used compressor at your local auto salvage yard or i would look on ebay to see if there is a good deal on one there.
Customer :I can probably change the compressor myself. I'll know more tomorrow.
Expert :The compressor is not hard to replace and I think you can handle it. There are a few more things we can check if you woudl like so you do not have to pay some one to look at it for you.
Customer :What else could I check?
Expert :the next thing to check will be the air out put of the compressor. You can pull the air hose out of the compressor and see if after jumping pins out in the plug in the trunk if the compressor is pushing out any air to the air springs.
Expert :The compressor has three parts to it, the compressor, the storage tank, and the solenoid body that controls what air spring has air directed to it.
Expert :Also there are control valves on top of each air spring that can be bad.
Customer :Ok, will the whole unit pull out without disconnecting any air lines because when I look at it I can't tell.
Customer :I see the tank and solenoid
Expert :You may be bale to pull it up some with out pulling the air lines loose. How many air lines are there on the unit?
Customer :Not sure but I think I see a total of four ports in an aluminum square block at the bottom of the tank. Not sure but there is a single rubber line at the top of the tank but it I am sure it is not a pressure line.
Expert :the air tubes for the air springs will com eoff of the top of the holding tank.
Customer :I can take a better look at the tank and line sand try pulling it up a bit to take a better look-
Customer :How late are you on tonight?
Expert :will be here till around 1 1pm
Expert :here is a diagram of the compressor.
Expert :The nuts and bolts that hold the comprssor in are removed from under the inner fender.
Expert :and there is one that runs through the comprssor from the top side. the diagram shows there locations.
Customer :Okay - thank you for all your help, I checked with my local mechanic here and find out the compressor problem.The sustpect either a leak or the compressor isn't working.
Customer :Problem resolved, the leaking line was replaced and compressor replaced.Thank you again, I think this service is a great deal and you were a big help -
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