206 speedometer and airbag warning

Hello there,
As much as I have seen in the forum, many of our friends have experienced similar problems I have experienced.
The speedometer of my 206 model car has been on the road for about a year. Sometimes he can start working again. After a while when the speed indicator stops, the airbag light comes on. When the car is parked while the key is on, the speedometer is moving even though I do not gas, as if I am on the road. I guess there is a problem in the brain of the car, what is your prediction experience.

Thank you for your answers and directions.

First, measure the charge of the vehicle. may be more

There is a 70 amp battery, could it be related to the problem?