Rear Window Heater

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2009 Jaguar XKR, 2009 Jaguar XK8, 2008 Jaguar XKR, 2008 Jaguar XK8, and 2007 Jaguar XKR. However, it is still accessible from the selected car via links, so may be relevant.

The automatic temperature control (ATC) module controls operation of the rear window heater using a relay in the auxiliary junction box. When a request is made for rear window heater operation, the automatic temperature control (ATC) module broadcasts a message to the auxiliary junction box on the medium speed controller area network (CAN) bus. On receipt of this message, the auxiliary junction box energizes the relay by providing a ground path for the relay coil. This allows a battery feed to flow across the relay to power the rear window heater element.

NOTE: Rear window heater operation is only enabled when the engine is running.

There are 2 modes of rear window heater operation; manual and automatic.

Manual operation is activated by pressing the rear window heater control switch. When the switch is pressed, the automatic temperature control (ATC) module illuminates a light emitting diode (LED) in the switch and powers the heater element for 21 minutes.

The switch light emitting diode (LED) remains illuminated until the rear window heater switch is pressed a second time (to switch the system off), the heating phase is completed, or the engine stops. If the engine is re-started within 30 seconds the rear window heater resumes the previous heating phase.

There are 2 variants of automatic operation; automatic operation at the start of a journey and automatic operation during a journey.

Automatic operation at the start of a journey is initiated if the ambient air temperature is below 5 °C (41 °F) at the start of a journey. In this instance, the automatic temperature control (ATC) module will automatically power the rear window heater element and illuminate the switch light emitting diode (LED) for 21 minutes. The rear window heater can be switched off during this period by pressing the control switch or stopping the engine.

Automatic operation during a journey is initiated when low ambient air temperatures are experienced and the vehicle has been travelling for a set period of time above a threshold speed. In this instance, no feedback is given to the driver to inform him the rear window heater is operational (the switch light emitting diode (LED) is not illuminated) and the duration of operation is variable depending upon the ambient air temperature, vehicle speed and the amount of time the vehicle has been travelling.