Hello! I am new. My puppy refuses to go potty anywhere besides the back yard.

I have a 5 month old miniature schnauzer. When he was a baby and I took him out to go potty, he would always go potty. Whether we were at a park or a friends house he would just eliminate himself before going inside. Recently now though for some reason he ONLY wants to go in the back yard. When I take him out to a friends house, he will hold it in for over 6-8 hours before he can?t hold it in anymore and pees himself inside, or until we get home and he runs to the backyard. I have tried crate training, and he will still hold it in for about 6-8 hours until he absolutely has to go. He knows the command go potty cause in the back yard when I tell him to go, he will go right away. I?ve tried taking him on walks over an hour and he still will wait until we get home. I?ve tried the chicken broth method into getting him to go potty outside of our backyard and he refuses. In the mornings when he really has to go I will drive him to other neighborhoods and he will pee, and I will praise him prefusively and give him a treat. But he will only still go if he has to. I?ve walked him with other dogs to show him to mark territories and he still won?t go. I?ve taken him to dog parks and places other dogs have peed and he will sniff and sniff around but won?t go. Around the neighborhood he went potty because I would take him in the mornings when he really needs to go. But whenever I take him with my to road trips he will NOT go. I am going to Temecula soon and don?t want him to pee at the guest house, and I want him to go potty during the road trip stops so he doesn?t relieve himself in the car. Is there anything I can do?!