When I press the brake it sound air and go down little

Hi Michael,

More than likely this is the brake booster. Do the brakes operate normally? If you have the engine off and you press the brakes, you will probably get 1-3 presses of the pedal before the vacuum is gone and the pedal gets hard. If this is the same noise you are hearing and the brakes are working then I suspect this is a normal condition.

Hello and welcome to 2carpros. Can you upload a video of the sound when you press on the brakes? I am asking because the GX does not have a brake booster? It has an acuator which is hydraulic and electric controlled? Attaching image.