I trained Muffin and now Kacee to use pads and then transitioned to outside.
She rings the bell to go out. Never fails. However, if we can't get to the door or we are gone, she will go use the pad and that is the only time she will use the pad.
I won't take her outside at night or in rain or other bad weather, so I have pads in the attached garage
(I know) and so at night when she goes to ring the bell I just ask her if she wants to go out in the garage and she follows me to that door.
It worked great with Muffin and I couldn't see why another genius yorkie couldn't learn that way.
So far it has worked out fine. Kacee is now 6 months old. No accidents in three months, but then again there is always someone home with her during the day, too.
Wishing you luck...