Does the car actually have a hydraulic (it would not be air) suspension system? If it does there will be little spheres in the back and a arm/valve connected to the subframe and chassis....also, there would be a hydraulic oil reservoir/tank under the hood with lines etc...

If it does not have those things, it just has a normal suspension....and sitting low can be caused by tired springs (common) compressed spring pads (common), dead shocks, and a worn differential mount and subframe bushings. I gained about 2-3" back on my car when I replaced my rear springs/spring pads/shocks.

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