I don't know. In the past I have come to the conclusion a sensor is bad from the troubleshooting process of elimination. In your case, I would eliminate the compressor as the problem first. Since it currently won't run it is at least part of the problem. If you applied current directly to the compressor with all electrical connections to the compressor disconnected it should run. If you remove the main output line from the compressor you can finger check the compressor PSI output.

Once the compressor issue is resolved I would eliminate the coding as an issue. Then you can eliminate the relays as the problem by disconnecting the links and moving them so the electronics think the suspension is too low. That should cause the compressor to run.

That seems to me to be a logical order to troubleshoot. Relays aren't that costly but I try to never buy parts I don't need. As one case only, I have never changed a suspension relay in 123,000 miles. However, my X5 has been in Texas all of its life and never subjected to salt, nor does it rain that often so they are corrosion free.

Even if the compressor needs to be replaced I think there is another problem to address. It may be the relays but the symptoms could also be a leak in the system. Obviously, most likely on the side that won't rise up at all. Coincidentally, Our X5M currently has a bad air spring. At first only that side would drop down after sitting a couple of days. Then it progressed to every day and then the good side started to drop some. Finally they both started dropping all the way down. Initially, a soap test did not identify a leak. It still inflates both sides properly but won't stay there long. Yesterday, I checked again. I didn't need to do the soap test, I could hear the leak. Sometime ago I replaced the bags on our 2002 X5. They dying process was the same.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas