Glow Plug
WARNING: This page is about a different car, the 2019 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.
The glow plugs are a low voltage ceramic type, At the tip of the tubular heating element is the heater coil. Behind the heater coil, and connected in series, is a control coil. The control coil regulates the current to the heater coil to safeguard against overheating.
It is important that the correct torque setting is used when refitting a glow plug into the cylinder head.