I have the same problem.. well only for a few days now. It might be a trouble with your baseband firmware. There is some version for different countries and operators...
I live in France, I bought one from Australia. It has been 2 years now i have it but, only since few days, it doesn't for in 4G/LTE and 3G. I think this is the problem, because I had sometimes this trouble but not for long. I live in Paris, it works, but I'm back in town for fews days, I do have 4G/LTE on other smartphone but not with my galaxy S4... I gonna try to change and see...
Good luck !
Cette réponse a-t-elle été utile ?