The four groups of parts in the air suspension (compressor, valve block, ride height sensors, air springs) work together, and any weak link causes a fault message, an uneven ride height or a car that settles. The characteristic symptom: the car sits down on one corner overnight, levels itself for minutes in the morning, and the compressor runs long and loud. According to the reports the compressor lasts 80,000 to 100,000 km; and a leaking air spring takes the compressor with it, because it keeps trying to make up the loss.