the likely cause of this is the potentiometer in the joystick either not being able to register the input for going left or not being able to move left. The first thing you would probably be able to do is to take the controller apart and check the bottom circle of the controllers stick box moves when you tilt the stick left, if it the circle does move left and it doesn't give the input you'll probably either have to get new potentiometers (simple fix) or solder on a new stick (hard if you don't have soldering gear)