I have S320 2002 model the problem is that it stays very low though there is no warning message.

An adjustable suspension is designed to give you better handling, manuvering and stopping power under different conditions. For instance, a higher setting, will be used for unpaved or rough terrain. This gives better ground clearance, and is designed for lower speeds. The median setting would be ideal for Suburban roads, where you will adjust to speeds between 25 and 55mph. The lowest setting, designed to lower the center of gravity of the vehicle, reduce the space between the under-carriage and the road, is meant for high speed. Speeds of over 55mph. This gives the vehicle better handling and lower profile which reduces drag. For the problem you're having, you should take the vehicle to a qualified dealer and have them run a troubleshooting test on the suspension system. Several problems could be apparent. An air valve is stuck open or closed, an electrical switch problem or a computer controller problem. Any of these could be an issue. I hope this helps.

Thank you very much for taking out time for me, you are a great help.

That chassie is notorious for front air shocks problem Check for oil deposit on shock boot About $1400.00 a side + labor