I don't know about this specific fan motor but in general. If you can get to the plug or wires Ohm out the fan speeds from Common to the other speeds. IE:1,2,3,4 if you only get resistance on 4 this is your issue. All speeds should show resistance. If 1-3 show a open (IE no resistance)the fan winding is bad for this speed.
You can also meter what is being sent to the fan from the feed with a meter. You should get some sort of voltage at all speeds.