Oct 19, 2015 · Reductant System . System Components . The reductant tank stores the reductant. The reductant tank filler hose is a 2-piece design consisting of a filler hose and a vent hose. The reductant pressure line supplies the reductant from the reductant pump assembly to the reductant injector. The heater element operations is not the simple result of readings from the temperature sensor in the active tank but is a more complex interaction of active tank temperature and ambient temperature. There's also two heater elements: one in the metering valve and one in the tank.