Comment by ErroneousBosh

From experience if the air suspension ECU freaks out over a sensor reading out of range it's either water in one of the connectors, or the sensor is getting a bit worn and you've run it to the far end of its travel.

Getting the vehicle four-square (possibly jacking up the corner with the faulty sensor so it sits about the right height) and resetting the EAS ECU with a diagnostics tool will solve the problem in the short term.

The other thing of course is you can just get it to sit level or at least level-ish, then unplug the ECU, let it complain about some unspecified fault, and drive it without self-levelling until it can be repaired, probably when you're not knee-deep in mud.