Technically the car should be safe to drive. If your car truly is fixed, you still may need to clear the check engine light code. You can do this by removing the negative battery cable for 5 min or so. If the check engine light comes on again, you need to take it Autozone or Oreileys and they can check the code for you. Perhaps the shop didnt fix the fuel issue. I don't understand the fuel additive level? What is that? Do you have the code # you can tell us?

Sorry no I do not have the code - all I saw was the Fuel Additive Tank level low. On google I have searched and many people have asked about this. My car is a diesel engine and apprently the additive helps the emmisions? I will try to remove the battery cable and see if this helps at all.

There are additives that you may have to run according to the diesel fuel that you run. I am not overly familiar with the sulfer issue but my next best guess would be to call the dealer and ask what additive (talk to a service technician) needs to be added where if you cannot find it on the internet.