another freaking battle
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Junior User
Joined: Feb 2014
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another freaking battle
I have a 99 expedition 5.4l around 80k on engine and 140k on body. Driving all day yesterday from fishing spot to fishing spot with my wife truck was perfectly fine. Finish up r day to head home and were dragging the *** of the truck all the way home. Compressor will not kick on and fill up the back. Get home check for power yo the compressor and I got nothing. all fuses and relays in and under the hood all fine. Check the relay plug behind the bumper it looks good. Pull the plug I have constant 12v on the first fat wire, connect it to the fat wire next to it hey compressor turns on. First thin wire next to fat wire has constant ground. But the last thin wire which is signal ground has nothing. Can't get anything from it no matter what I do. I read that wire controls the air suspension module. Is that right? And where the hell is it? I got the compressor to kick on by connecting the wire but I have no power to the compressor only ground and I can't get the back bags to inflate even when I force the compressor on. Oo the switch inside on pass side is also switched to on. Can anyone freaking help me with this please.
Fleet Owner
Joined: Apr 2008
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The air compressor relay you found behind the bumper could be bad. You need to connect a tester to the two small wires and then have someone get in, start the engine, open and close the door, then shift into Drive. This should trigger the air suspension module to turn the compressor on. If it does not you could have a bad height sensor. If the front is pumped up to normal, then it could just be the rear height sensor.
New User
Joined: Apr 2015
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I think the solenoids have to open up for the air to go in, so even if the compressor runs, the air can't make it into the air bags.
Did you try to plug the relay in afterwards to see if it would come to life? When I had this problem, it worked right after I plugged it back in for a week or two. I guess the fix would be a relay, and/or the suspension compressor relay connector.
Did you try to plug the relay in afterwards to see if it would come to life? When I had this problem, it worked right after I plugged it back in for a week or two. I guess the fix would be a relay, and/or the suspension compressor relay connector.
Freshman User
Joined: May 2004
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I had the same problem on my '98 XLT. The relay was bad and I spent hours tracing wiring first. One quick and dirty way to check the height sensor is to have someone start the truck with the doors close, you should hear the solenoids "click open", if you don't it might be the sensor b/c the computer isn't opening them to fill the bags. If they do open you can then jump power to the compressor across the relay (use a heavy gauge wire with good insulation it will get hot) and the bags should inflate and if the solenoids click close before you are at full ride height then it is bad, if they fill to ride height then close most likely the relay. This seemed to work for to determine it was the relay. My LLS system worked great until about 150K then everything started going wrong, bags, lines, relay, comp. If you think you are going to keep the truck for while I would consider changing it over to springs. The guy at Suspension Conversions & Air Suspension Parts for Most Makes & Models has kits and parts and is real friendly with just answering questions as well. Good luck.
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