The official explanation is:
HEATED REAR WINDOW
Heated Rear Window (HRW) operation is only enabled when the engine is running. The
ATCM controls operation of the heated rear window using a relay in the Rear Junction
Box (RJB). When a request is made for HRW operation, the ATCM broadcasts a
message to the BCM/GWM assembly on the HS CAN power mode zero systems bus. On
receipt of this message, the BCM/GWM assembly 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 heater element.
There are two modes of heated rear window operation; manual and automatic.
Manual operation is activated by pressing the HRW switch. When the switch is pressed,
the status Light Emitting Diode (LED) in the switch illuminates and the rear window
heater element is energized. Manual operation is discontinued when the HRW switch is
pressed a second time, between 5 and 21 minutes have elapsed (dependent on
ambient air temperature), or the engine stops. If manual operation is discontinued by
the engine stopping, the previous heating phase is resumed if the engine is re-started
within 30 seconds.
There are two 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 for between 5 and 21 minutes
(dependent on ambient air temperature). The higher the ambient air temperature, the
shorter the time. In this instance, the switch LED is illuminated and the heater element
is energized. In addition to shorter operating times in temperate winter conditions,
there are condition qualifiers to prevent subsequent operations once the cabin or
engine is warm, or there is a significant sunload. Automatic operation is discontinued if
the HRW switch is pressed or the engine stops.
Automatic operation during a journey is initiated when low ambient air temperatures
are experienced and the vehicle has been traveling for a set period of time above a
threshold speed. In this instance, no feedback is given to inform the driver that the
HRW is operational (the switch 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.
HEATED WINDSHIELD (IF EQUIPPED)
Heated windshield operation is only enabled when the engine is running. The ATCM
controls operation of the heated windshield using two relays in the Engine Junction Box
(EJB). When a request is made for heated windshield operation, the ATCM broadcasts a
message to the BCM/GWM assembly on the HS CAN power mode zero systems bus. On
receipt of the message, the BCM/GWM assembly energizes the relays by providing a
ground path for the relays coil. This allows a battery feed to flow across the relays to
power the left and right heater elements.
There are two modes of heated windshield operation; manual and automatic.
Manual operation is activated by pressing the heated windshield switch. When the
switch is pressed, the status LED in the switch illuminates and the windshield heater
elements are energized. Manual operation is discontinued when the heated windshield
switch is pressed a second time, between 2 and 5 minutes have elapsed (dependent on
ambient air temperature), or the engine stops. If manual operation is discontinued by
the engine stopping, the previous heating phase is resumed if the engine is re-started
within 30 seconds.
There are two 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 for between 2 and 5 minutes
have elapsed (dependent on ambient air temperature). The warmer the ambient air
temperature, the shorter the time. In this instance, the switch LED is illuminated and
the heater elements are energized. In addition to shorter operating times in temperate
winter conditions, there are condition qualifiers to prevent subsequent operations once
the cabin, engine or screen is warm, or there is a significant sunload. Automatic
operation is discontinued if the heated windshield switch is pressed or the engine stops.
NOTE:
This feature can be selected on and off on the Settings page of the Climate
menu in the Touch Screen (TS).
NOTE:
Automatic operation during a journey is initiated when low ambient air temperatures
are experienced and the vehicle has been traveling for a set period of time above a
threshold speed. In this instance, no feedback is given to inform the driver that the
heated windshield is operational (the switch 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.
23 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021 > D5 HSE Dynamic D350 2025
