Check Suspension light on 1998 expedition ON.

[bigallant]

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.

[jgate]

For a better understanding of what your problem is, read the DTAC from the module.
DTACs
B1318 Air Suspension Control Module Battery Voltage Low
B1342 Air Suspension Control Module ECU Is Defective
B1485 Air Suspension Control Module Brake Pedal Input Circuit Battery Short
B1566 Air Suspension Control Module Door Ajar Circuit Short to Ground
B1749 Air Suspension Control Module Park/Neutral Switch Circuit Failure
B2140 Air Suspension Control Module Initialization Failure (Vehicle Ride
Height Not Programmed)
C1439 Air Suspension Control Module Vehicle Acceleration EEC -IV
Circuit Failure
C1724 Air Suspension Control Module Air Suspension Height Sensor
Power Circuit Failure
C1725 Air Suspension Control Module Air Suspension Front Pneumatic Failure
C1726 Air Suspension Control Module Air Suspension Rear Pneumatic Failure
C1756 Air Suspension Control Module Air Suspension Front Height Sensor
High Signal Circuit Failure
C1760 Air Suspension Control Module Air Suspension Rear Height Sensor
High Signal Circuit Failure
C1770 Air Suspension Control Module Air Suspension Vent Solenoid Output
Circuit Failure
C1790 Air Suspension Control Module Air Suspension LR Air Spring
Solenoid Output Circuit Failure
C1795 1 Air Suspension Control Module Air Suspension RR Air Spring
Solenoid Output Circuit Failure
C1830 Air Suspension Control Module Air Suspension Compressor
Relay Circuit Failure
C1845 Air Suspension Control Module Air Suspension Front Inflator
(Fill) Solenoid Output Circuit Failure
C1865 Air Suspension Control Module Air Suspension Rear Inflator
(Pill) Solenoid Output Circuit Failure
C1869 Air Suspension Control Module Air Suspension Gate Solenoid
Output Circuit Failure
C1917 Air Suspension Control Module Steering EVO Out-of-Range Fault
P1808 PCM 4x4 Low Indicator Circuit Short to Ground