I have a 1998 Ford Expedition EB. 140K miles, car still runs great. Recently I noticed the “Check Suspension” light came on. It will stay on until I turn the car off and turn it back on. It will stay off for a while, then turn on again. I also keep hearing the compressor motor activating periodically (more often than it used to) several times during the day and during a drive. Sometimes I’ll hear it activate and it will lower the back of the car, sometimes it activates and raises the back, seems the front is not affected. At times I’m not even in the car and I will hear it activate. (1) Since the compressor raises and lowers the car, I suspect that the Compressor is OK. (2) I’ve noticed that most of the times when the car lowers, is when the compressor activates and lowers it, so, I suspect I do not have a leak in the air bags. (3) Am I safe to make these two assumptions? (4) Can I assume it is a sensor? I will need to check to see where they are located. (5)What is the best way to diagnose this problem. Thank you.