Auto Adjust Suspension on GXL
 

Any body know how to test the auto adjust suspension is working or not? If not, how to fix? Thanks!

Drive it. Put it on normal and start making some hard slalom like turns and then switch it to sport and do the same. You can feel a difference; sport won't have as much body roll.

Don't fix it, just replace it, the oem replacement parts are too expencive. Just chuck everything out and put whatever you want in.

Don't waste your time. It's probably long past worn out, and it is generally agreed that the auto adjusting suspension is nothing more than a gimmick. Replacing with dealer parts will probably cost several thousand, so simply get a good aftermarket setup. It will be vastly superior.

It depends exactly on what you mean by 'working'.
If you want to know if it is working electrically, the easiest thing to do is remove one of the covers on the front shocks. Under you'll see a small stepper motor. The centre shaft of the motor will turn a bit (~20 degrees) when you switch between normal and sport. If necessary, mark the shaft with a dab of paint to see the movement.
If you want to know if the AAS computer is working, that's more involved. It accepts inputs from brake fluid pressure sensor, throttle position switch, road speed sensor, etc. and switches the shock settings through three different levels. You would have to rig up a test light or multi-meter and do a dynamic test.
Lastly, if you're wondering about the mechanical condition of the shocks, you'll have to look for leaking oil from the body of the shock, or rely on the subjective 'feel' of the car as it travels over bumps, etc.

Start the car. Have someone move the switch between sport and normal while you jump on the bumper. You'll know if it is working.

As said above, throw it away. If you a serious about performance, change out your shocks and springs. These are worn out by now and you'll feel a world of difference. I personally put in some seven way adjustable Apexi shocks. These took a lot of the slop out of my 125k ride. A few months later, I put in some Eibach springs. This setup is rather harsh, but it is worth it at least it is to me.