100,000 miles on car, air suspension fault light goes on.

This can be somewhat complicated to solve accurately without a high end scanner and more info on your vehicle. Does your vehicle appear to be sitting at the proper ride height? Are there any other warning messages on your dash (for instance "vehicle too low") ? The most likely scenario is that one or more of your air shocks is leaking air and causing the air compressor to have to run too long in order to maintain the height of your vehicle. I would hate to give you bad advice, but typically after some initial diagnostic checks, which rule out other issues, I end up recommending that all four air shocks be replaced with conventional shocks. A company called Arnott makes a conversion kit complete with four conventional shocks and a "spoof module" to send a false signal to the vehicle computer so that the vehicle believes that the air shocks are still installed and working properly. The conversion kit tends to be the most reliable way to keep the vehicle at the proper height, and keep the light out, with the added benefit of being cheaper than replacing the air shocks, and later the compressor (they fail sometimes too). If you wish to keep the air shocks, Arnott also makes replacement air shocks for many Jaguars. If you do identify a leaking shock, and decide to replace only that shock with an air shock, keep in mind that you will be back to the mechanics in a very short time to do the other shocks, as they are all the same age and most likely in the same (near failure) condition. (strongly advise not doing one at a time, you are not likely to succeed in saving money this way) Hope this helps