Most icemakers of today are the half moon heat release style icemakers. The water valve is designed to let only a certain amount of water to flow in a given time period. You can count the seconds that the valve is operated. If the timing is correct, then the valve is at fault. If the timing is incorrect, then the icemaker is the problem.
Repair is to replace the module or the complete icemaker.
For more information, go to the link at the top of the page on the service sheet for modular style icemakers.