I have a 2000 Navigator with the lls. The check suspension dash light is on. The rear axle sags. I replaced the compressor, compressor relay (twice), and replaced a level sensor that the electric board looked brown, replaced all fuses (all looked good but was worth a try). I took it to a Lincoln shop and they wanted to replace the module. Talked to another shop and they said modules rarely if never go bad. I have the relay harness jumpered with a switch to manually turn the compressor on. Compressor runs fine, and will lift the rear end. The relay in, control for a lack of a better word only has 4.4 volts or so, not sure if this would affect it? The rear axle bags stay inflated for a day or two before I have to air up again, slow leak I guess or system still vents when doors open. Is there a way to test the relay, or is something else out. I tried disconnecting the battery to reset the system. I'm lost.

 

Welcome Orange Crush. As you can see, I have the same vehicle as you, and to me, it certainly sounds like you have a leak. I would serach for the union connector that is on a white 1/8 inch air line that runs beneath your master cylinder. Let's start with replacing that. You might try some soapy water on it (and all the other line connectors) first. It could be one of the air bags itself. Just work the problem one component at a time.

 

Listen to this guy, He knows what hes talking about.