I had this happen with my 1999 Expedition. There was a cracked air line under the hood. The air line ran from the compressor to the rear "air bags," which are not really air bags but more like an air spring that holds up the rear of the car.
The local Ford dealership locate the break in the hose, and fixed it for about $100. I got lucky - it could have been more expensive. The air shock itself can be several hundred dollars. So can the compressor. It also could be something like a sensor, which is fairly cheap (under $50). Anyway, good luck.
If you are wanting to rid yourself of a bunch of headaches and wallet crunching, check out Strutmasters. I bought a non air conversion kit from Strutmasters for my 2002 Expedition and it worked great! The ride is good the price was even better. If you hare having issues with your air already it wont be long before something else will go on it and it could cost you up into the thousands to fix. Grab the bull by the horns and take care of this problem air ride.
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how do i find the compressure for my rear suspension? or any possible issues for rear air suspension wire issues.
Check the Height Sensor.
Check for leaks on the air lines. Or holes in air bags
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Your suspension is probably shot. Check your shock absorbers.
Check owner's manual. If you don't have one copy and paste link below; www.fleet.ford.com/maintenance/owners_manuals
Check your owners manual. If you don't have one copy & paste this link. http://www.genuineservice.com/genuineservice/en/gloveboxresults
Check wiring again. Check for bad ground. Recheck all connections.
Air Suspension switch is located in the PASSENGER SIDE kick area. Check owner's manual. If you don't have one copy and paste link below; www.fleet.ford.com/maintenance/owners_manuals
For this answer you will need to either use an OBD code reader or go to a shop that can read codes. Also make sure that your air suspension switch is turned on.
Under the hood on the passenger side front corner. If you are having trouble with you suspension and would like to get some answers please go check out Strutmasters they are really great and will be glad to help you with any of your suspension parts and shocks and struts.