I trained Minnie on the pads and I'm so happy about it. She relieves herself whenever she feels like it and it's great cause I don't have to worry about taking her out when I'm not at home. She also goes outside when I walk her, and that was something she picked up on her own. But since your puppy won't go outside on the grass, this is a tip I heard from a friend:
When your puppy pees, soak the pee in a newspaper and take it outside immediately, along with your puppy. Place the soaked newspaper on the grass and let your puppy smell it. Repeat this a couple of times/days and hopefully it will be a success..
to you.