ECT 1
WARNING: This page is about a different car, the 2011 Jaguar XK and 2010 Jaguar XK. However, it is still accessible from the selected car via links, so may be relevant.
ECT 1 is installed in the heater manifold, at the rear of the right-hand (RH) cylinder head. The input from this sensor is used in calibration tables and by other systems.