It's behind the control panel but the problem is more likely that the pressure hose is clogged with gunk. Remove the front panel of the washer and with washer empty, unplug the hose from the air dome on the lower left side of the tub. Be careful not to break the hose nipple off. Clean any gunk out of the hose and the air dome as well. The dome is not removable so you will need to flush some hot water through it using a turkey baster or similar to clean it out. You can check operation of the pressure switch by starting a fill with hose disconnected from air dome and blow gently into the hose to activate the switch which should cut the water flow off. If it won't work, there may be a leak in the hose or the switch is defective.

Eric