Could be trouble with AYC. When was it last flushed?? maybe start with a flush then go from there if its still on. I'm sure someone with more knowledge than me will help more though
Alan if it comes on straight away and stays on that's PROBABLY a pressure switch fault. You can start by checking your diagnostic codes and seeing what that has to say though, there's a thread called 'sensor codes the full list' or something which describes the process of putting the car in diagnostic mode and working out what they mean.
Usually with air in the system you'll get the AYC light coming on after a while, sometimes intermittently and sometimes after getting the AYC activating by driving round corners at speed.
The big problem is if its not the pressure switch but in fact the AYC pump itself - in that case you're up for not insignificant dollars, unfortunately