Thanks for the reply sir.
Actually all the connections are proper & LCD displays all the messages perfectly until the speed of DC motor is constant.
As soon as we switch the position of knobe on DC Fan from low to high or vice versa; the LCD starts showing some garbage characters after sometime. I guess this is a kind of EMI / inductive effect of back emf generated by DC motor which is forcing LCD to go uncontrolled & show some garbage values..
What do you say?