When you connect your Samsung Galaxy S5 with the hands of your car, for example, an Audi, a BMW, Porsche etc then it can happen under certain circumstances, that you can use the phone feature of your smartphone through your car, but not the mobile Internet on the device itself.
Background is the so-called SIM Access Profile service on the speakerphone of your vehicle. This uses using Bluetooth SIM card for the phone module integrated in the vehicle.
This is similar to a withdrawal of the Sim card from your Samsung Galaxy S5, so you then can no longer surf the mobile Internet. A message such as "No service" etc. appears on the display of the Samsung Galaxy S5, although making a call using the speakerphone or the Multifunktionsnavi your vehicle.
For more information about the SIM Access Profile can be found at Wikipedia.
Now you know why you can not use the mobile Internet on the Samsung Galaxy S5, when it is connected via Bluetooth to the navigation device and the phone module of your vehicle.