Hi,
Does the Volvo v40 2002 has a steering force system?
the steering seems very sensitive when driving with high speed.
If there is no such a system in this car, what makes the steering wheel very light and difficult to control?
wheels presseur/ alignment/ suspension are all checked and okay.

 

Are you meaning 'a power steering system'?
If so, yes they do have power steering.
I also have a V40 2002 and I have always considered the power steering to be relatively heavy as compared against many other modern vehicles.
I quite like it as it gives a sense of being a firmer, positive, yet power assisted system.
Many modern cars of course have electric speed sensitive power steering systems as opposed to a hydraulic system as our V40's have.
It would be a good idea to check the fluid level of your car if you feel something as altered recently.

 

The problem is that the system stays sensetive all the time. While parking or speeding on the highway. I thought of a damaged sensor that controls the sensetivty of the power steering according to speed. In moderen Volvo's you can adjust this manually.