Auxiliary Coolant Pump
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2015 Jaguar XFR, 2015 Jaguar XF, 2014 Jaguar XFR, 2014 Jaguar XF, and 2013 Jaguar XFR. However, it is still accessible from the selected car via links, so may be relevant.
On all vehicles except 3.0L, an auxiliary coolant pump is installed on the rear right side of the radiator housing, in the return line from the heater core. The auxiliary coolant pump is an electric pump that boosts the flow of coolant through the heater core.