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99 Expedition Air Suspension Problem


Old 11-29-2005, 11:28 AM
Thread Starter
Join Date: Nov 2005
Location: Madison, WI
Posts: 12
99 Expedition Air Suspension Problem

I am having a problem with the air suspension on my 99 Expedition. I bought the truck used a year ago. A friend of mine told me about this forum. Not sure if I should post this to this group or the Expedition board. Here is my problem:

The air suspension does not seem to be working. When I first start the truck, the "Check Suspension" light is *not* lit. After about 5 minutes or so, the light will illuminate.

During this time I do not hear the compressor kick on at all. In the past I could hear the compressor kick on and run, so I know what it "sounds" like. Now, though, I cannot hear the compressor running.

I took the truck to my local Ford dealer in Madison. They charged me a $75 diagnostic fee and told me that I needed a new compressor. They wanted $625 with labor to replace it. Since I'm not totally clueless when it comes to vehicles (and my friend is a big Ford guy who knows how to do all this stuff) I said I would take a pass, figuring I could get a decent aftermarket compressor myself and my friend will help me install it for a case of Sam Adams.

Now, this is where it gets funky. I ordered an aftermarket compressor on Ebay for $200. I go over to my buddy's house, and in 3/4ths of an hour we have the old compressor out and the new one in. Great! I've saved $400!

But wait... I start up the car... and... The compressor doesn't kick in. Same symptom as before (no Check Suspension Light upon vehicle startup, illumunates about 5 minutes after the car is started).

Hmmm... We take the old compressor, and apply 12vdc to it. The compressor chugs right along. We pull the new compressor out, apply 12vdc to it. Likewise, it chugs right along. Put the old compressor back in, apply 12vdc to it manually, and it pumps up the air shocks, no problem at all.

Ok, now what? My buddy pulls down some info off the web (alldata?), and we see there is a relay that controls the air pump. I don't know anyone else with the air suspension that I can swap the relay with, but it seems reasonable that the relay is toast. So I go back to the dealer and buy a relay. OUCH! $120! For a damn relay! But hey, I figure I'm still $300 ahead of the game from what the dealer wanted to replace the "defective" compressor which clearly wasn't defective.

I swap the relay on the truck, and it has no effect. Of course, the dealer won't do a refund since it is an "electrical" part and there are no returns/refunds on electrical components. What's the likelihood that I have a defective relay from the dealer? Very small, so I doubt that is it.

We did all of this work yesterday. I'm out of ideas now. We were able to manually pump up the air shocks by applying 12vdc to the compressor when the truck was running, so for the time being everything is pumped up and driveable.

But... What else could be causing the air suspension not to work? I'm baffled. Its not the ride height sensors, those clearly work since they pumped up when we "turned on" the compressor manually. It wasn't the relay. It isn't the compressor.

All that is left seems to be the Air Suspension computer, and I can just *imagine* what that costs.

All the wiring looks like it is in good condition. Is there a way to troubleshoot the wiring to see if I'm getting 12vdc to turn on when it is supposed to?

Does anyone have any ideas? I'm really hesitant to go back to the dealer, since they told me the wrong thing to start with.

Thank you,
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Old 11-29-2005, 02:28 PM
Senior Member
Join Date: Jun 2004
Location: Richmond, TX
Posts: 223
Well there is never much help in this section when it comes to the Expedition LLS. More people with LLS knowledge will read it in the Expedition Section.

Now on to your problem. I have to ask the obvious, Have you checked to make sure the switch is in the "ON" position? Sometimes it gets turned off by people, or the accidental wondering foot. If it is on, then lets move on. I did not see that you tested the relay. You can do this by applying 12v to the 2 large wires on the relay. This is much the same as what you did to test the compressor. You can also test the "signal" from the LLS computer to the relay by reading the voltage on the smaller wires. I can not remember off the top of my head what an "OK" reading would be, but I am sure it can be found with a search. I am not sure what else to look at besides that computer. As an FYI, this site http://www.strutmasters.com/ has good prices on parts for the LLS system. They also have many parts they do not list on the site.
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Old 12-01-2005, 11:57 PM
Senior Member
Join Date: Oct 2005
Location: Central MA
Posts: 104
I'm going from memory here so I may miss some of the deatils but there should be a height sensor on the front and the rear. I know there was one on the left front (I can't recall if there was on on the right front too but I doubt it). The front one is connected to the upper control arm but I can't remember where the rear one is located.

It's a longshot, but maybe one of the height sensors has gone bad and is causing the Check Suspension light to come on.

I wish I could remember more (I recently traded my '97 Expy in for an '06 F150). Fortunately, I never had any problems with the LLS

Good luck.

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