Hi Dan, thanks for your help. Just an fyi, I live in Michigan, and it's about 25 degrees outside, so this is likely a weekend job for me. That's why it took so long to get back.
Right now, I suspect that I would need to review the following links:
Diagnostic System Check - Air Suspension
Air Suspension Description and Operation
Rear Air Spring Level Sensor Calibration
Air Spring Leveling Sensor Replacement.
I am familiar with the Air Suspension, but the link info might be helpful to the repair, assuming sending same not too much trouble.
The inflator works. I can hear the compressor kick on. Twice in the last two weeks it has inflated, stayed inflated for a few hours, then deflates, so we know the compressor works.