Actually it WILL autofocus if I force adjust focus by hand beyond subject. It then adjusts itself to focus. If the lens is focused in front of the subject, it will not autofocus. Bad servo in the lens?
If you think the motor is only working in one direction, you might try to test the theory by focusing in live mode. If it's like mine, it will usually go back and forth to home in on the sharpest focus (using contrast rather than phase detection), so if the motor is only working in one direction it will probably not be able to focus in live mode.
Of course, if you have any access to a different camera, you could double check it on another camera to make sure the problem is in the lens. In any case, you'll probably need to send it in for analysis/repair.