What do you mean by on the fritz? I am assuming the fluid level is good with no bubbles. If there are bubbles in the PS fluid it could indicate a bad nitrogen cylinder on the brake booster. Usually you puke all the fluid out as well.
Another possible cause would be the filter on the pressure side of the pump. Do a search on this and you will find that there is a small in-line filter screen and check ball inside the pump that you can access.