I posted this originally to the suspension message base but those folks said I should post here since you all would be more familiar with LLS.

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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,
Vinny

 

Is the *** end of the truck sitting low? When you jump power to the compressor and it runs, you said it'll raise the rear end up...does it stay up? Does it leak down if you let it sit for a while?

 

The *** end does get low, but it takes a long time for it to happen (week+)

 

Check the air line union near the air filter box; it's prone to cracking/leaking, often times ultimately they break, flattening the suspension in a hurry. If the suspension module doesn't sense the rear raising when the compressor is running (because of the broken/leaking union), it'll minimize compressor run time or won't run the compressor at all as to not damage it. The union itself is like $10 or so. I wish I had a picture to describe, just peak around the air filter box and master cylinder area, it'll look almost like an electrical butt connector, black, with two air lines going to it on either end.

 

I'll check in the AM when I can see better. However, if this connection were broken, wouldn't the air suspension at least kick on initially when the truck is turned on? The reason I ask is even when the *** end is low, when I start the truck, the compressor doesn't kick on at all. Its as if it isn't getting any juice (which made us suspect the relay). From your description I would expect it to at least kick on for a few seconds and then perhaps shut off.

Vin

 

If I found the piece I think you're describing, it's perfectly intact and doesn't appear cracked.

This morning, I popped the hood while my wife was in the truck. I had her start the truck, put it in N, and then switch to 4WD LO. It is my understanding that this is supposed to tell the air suspension to pump up to its highest level. The air pump never turned on, not when she started the truck nor when she changed to 4LO.

I suspect an electrical problem or a problem with the air suspension computer. What else could it be?

 

Have you tried the relay test I mentioned in the other thread?

Or look to see if the switch is "off"?

 

Hm...all the doors shut? No errant door ajar lights or anything like that?

I'd hate to tell you that it's a module, then you run out and throw a module on it and we're back in the same boat we started off in.

 

Yes, all the doors shut. No errant door ajar lights. Everything you would expect to be in place for it to work. The switch isn't off (normally if the switch is off the Check Suspension light immediately lites up when you start the truck... whereas in this case, I don't get the light until about 5 minutes into the process).

In the other thread when you said "apply 12vdc to the two large wires". Do you mean complete a circuit between the two a-la 12vdc to 1 wire and the other wire to ground? Or literally apply 12vdc to BOTH wires? I meant to ask that. I got home too late tonite to do anything anyway.

What's a module? Do you mean the suspension computer? I'm hopeful its something easier like a loose connection

Thanks,
Vin

 

just take it to the dealers man, get your headaches out of the way with this one. Let the dealer figure it out!

 

Err... If you actually took the time to read my initial post, you would have seen that I *already* took it to the dealer, and the dealer's diagnosis was *wrong*.

So, what are you suggesting? That I take it to the dealer, let them charge me $625 to put in a replacement component I do not need, and *THEN* tell me "oh, you also needed a <insert name of the actual part that was broken here> which cost another $400"?

 

dealers LOVE people like Mountain...boy above.

Yes, complete the circuit on the relay with 12volts. The same way you did it with the compressor when you tested it.

If the relay is good, compressor is good, then your problem most likely lies in the LLS computer (module). The union talked about above will not give you the problems you are having, but it would be a good idea to replace it with the new style union or just get one and keep in the glove box.

Good luck.

Oh, if you do have to replace the computer, look at places other than the dealer. Go to places like Fordpartsonline, Strutmasters, etc. You can probably get the computer for 1/2 of what the dealer will charge you.

 

Thanks. Another person here sent me a couple of scanned pages from the Helm Vac & Electrical manuals which show a diagram of the LLS circuit. I think I understand it.

It appears that the solid state relay has 4 connectors - A B C D.

A is labeled as being connected to the power distribution box, always hot, on fuse #15, a 50 amp fuse. I can disconnect the relay and see if I have 12vdc on terminal A. If I do not, perhaps there is a problem w/ the wiring back to the distribution box or the fuse, where honestly I didn't think to look before). I can check continuity if I don't have 12vdc and see if there is a break in the wiring.

B is labeled as being 12vdc from the relay to the air compressor. Here, I can test continuity of the wiring from the relay to the compressor to make sure I don't have a wiring problem. Since B is switched by the relay it normally wouldn't be on unless their LLS computer says to switch it on.

C is labelled as a ground. I can test continuity here to ground on the chassis. If I have a bad ground, naturally the pump wouldn't turn on. Oddly enough, the diagram shows that the ground wire from the air compressor itself splices into this same line before it goes to ground, so I can eliminate two potential wiring problems at the same time.

Finally, D is labelled as 12vdc connected to the Air Suspension Module. I assume D is not normally energized unless the computer wants to pump up the system. So, this connector will normally be 0vdc unless the air suspension pump is being turned on. This line terminals at the 4WAS module, pin 18, so again with a little ingenuity I should be able to test continuity to make sure the wiring is secure.

If the wiring is secure, and I don't get 12vdc output on pin D when the LLS should engage the pump, I think its safe to conclude that the 4WAS module is toast, yes?

Does all this sound reasonable? I'm going to take a 1/2 day out of work tommorrow to try and fix it while there is still daylight.

Thanks for the tips on web sites too if I need to order another module. Is there a part # I should reference? The documentation another member sent to me doesn't show a part # for the 4WAS module.

Thanks again
Vinny

 

Here is a thread from another site the might help you a BUNCH on this. It will also give you additional info we have not discussed here. Read this before you start on this project.

http://www.ford-trucks.com/forums/sh...ght=lls+wiring

 

Thanks for the link! Interesting reading!

The 12vdc vs 7vdc across pins C and D of the relay is interesting. The scan of the HELM manual, page 41-1, clearly shows a little "12v" next to Pin D, while Pin C shunts to ground. Its interesting that others would measure 7vdc rather than 12.. The resistance reading on Pins C and D will be helpful too, although like I said before I doubt the relay itself is bad since it is brand new (although it isn't unheard of).

Although..the dude was getting 7vdc across pins C/D and his pump *wasn't* engaging, which would seem to imply that 7v is insufficient voltage to trip the relay. 7v may always be present until the module wants to activate the pump, and then it goes up to 12.

The ride height in the front and back both appear to be fine, especially once the system pumps up. It doesn't look like the front changes all that much, though, I honestly don't think its ever moved once that I can recall.

I guess what I'll do today is test the relay per my previous post, and then if that seems to accomplish nothing I can pick up another ride height sensor and try swapping it. Of course, I'd hate to buy a new one of those to and have it (again) not be the solution. Any ideas how to test a ride height sensor's operation?