Auxiliary Coolant Flow Pump
WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
An auxiliary coolant flow pump is used only on hybrid vehicles to improve engine coolant circulation, for heater operation, at low engine speeds or when the engine is OFF.
For a complete explanation of the auxiliary coolant flow pump refer to heating and ventilation in the Description and Operation portion of CLIMATE CONTROL -- FUSION, MILAN & MKZ article.