Thanks folks. It’s not air suspension but some kind of hydraulic setup. I think it works of the Hill start program. That’s a feature where you don’t have to hold the brake on a hill start. (Manual gearbox only) you press the clutch and brake pedal together on an incline, and the ABS stays on until the clutch is released. There is a sensor that’s picks up the incline, I suspect the self levelling suspension works from this. If you put a heavy trailer on the back just give it a few miles and things level out all by them selves. But you have to drive the car for it to work. Once you remove the trailer the rear rises but after a few miles all is back to normal?. I think you are correct, it’s probably a complicated job.