I'm surprised no one has responded yet. There are several similar posts on this forum. Use FIND to look at them. The general consensus seems to be the control panel at the dash being disconnected or loose. Check the wiring harness where it meets the control panel.
Are you measuring the air pressure at the rear drain outlet? You need to decide if the problem is a control issue, a compressor issue or an air line/air bag issue.
Once you narrow it down, the troubleshooting will be easier.
2003 Alpine 40FDTS (400HP)
Long Beach, CA