My boy did the same thing. He was about 1 or 1.5 y/o, and he would pee on the pad, but poop in hiding, like behind the couch
I taught mine using the word "go potty" for pee and "go pooh" for poop. I also give a yummy treat reward for good potty behavior. It really should not take long. If he already goes pee on the pad, next time he does pee PRAISE HIM, say good boy and give him a yummy treat (little piece of cheese may do the tick), once he starts to realize he will get a treat for doing pee on the pad, he will start to do poop on the pad too, because he wants a Yummy treat
