While driving, the 'Check Air Suspension' warning message came on and we noticed that the ride was a little more bumpy than usual. Once we arrived to our destination, the rear of the vehicle was sagging - the frame nearly touching the tires.

To check if the air compression was turning on at all, we turned the vehicle on, closed all the doors, and heard the compressor switch on (later found out that when the compressor is operating correctly, it should be pretty quiet). The rear of the vehicle did not come up at all.

This quick check meant that the air compressor relay was working and there was either an air leak or the air compressor was failing to build pressure.

Since the compressor would turn on but not build pressure, it would remain on. We pulled the fuse for the air compressor relay for our drive home. If it was an air leak and the compressor was good, we didn't want to damage the compressor by running it for too long.

We drove the vehicle home (very slow bumpy ride - avoiding highways) and took it to a local mechanic for an inspection. The mechanic found that the air compressor had failed, so he replaced it. The mechanic also mentioned that Ford keeps these compressors on the shelf - an indication that this is likely a common issue.