My check engine light has come on. I took it to a mechanic and he says it's the knock sensor. He also said the ball bearing for the transmission needs to be changed. He mentioned that fixing the knock sensor may fix the problem all together. Is that possible, does the knock sensor effect the transmission?

 

No, and there isn't a ball bearing in the transmission. If you have a manual trans there is a throw out bearing. If that's bad you would replace the clutch while you were in there.