LR3 (LA) V8-4.4L (2009)
Heated Glass Element: Description and Operation
Rear Window Heater
Rear Window Heater
DESCRIPTION
Introduction
Operation of the rear window heater is controlled by the Automatic Temperature Control Module (ATCM) using medium speed CAN messages. The
ATCM operates the rear window heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and
whether it is the initial or subsequent operation during the current ignition cycle.
When the rear window heater switch is pressed the ATCM illuminates an LED in the switch and initiates the appropriate heating cycle. The LED remains
illuminated until the rear window heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or the ignition is turned off,
rear window heating resumes if the engine is re-started within 20 seconds.
OPERATION
Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 11E and fusible link 17E (C0632) on an R wire. Both are located in the
Battery Junction Box (BJB). Fusible link 17E (C0570) is connected to fuse 13P and fuse 51P of the Central Junction Box (CJB) (C0583) on an NR wire.
Fuse 13P provides a constant battery feed to the rear window heater relay, which is also located in the CJB. Fuse 51P (C0582) provides a constant
battery feed to the ATCM (C2655) on a GP wire. The ATCM (C2655) is provided a ground path on a B wire.
Fusible link 11E (C0570) is connected to the ignition switch (C0028) by an N wire. When the ignition switch is in the ignition position, current flows
across the switch (C0028) to the rear window heater relay coil (C0582) on a Y wire. The ground path for the relay coil is controlled by the CJB.
Ambient Air Temperature Sensor
The ATCM (C1629) provides a feed to the ambient air temperature sensor (C0412) on a YN wire, and a ground path via a BG wire. The sensor is a
Negative Temperature Coefficient (NTC) sensor. By monitoring the voltage output on the YN wire, the ATCM can determine ambient air temperature
and control the operating time of the rear window heater accordingly.
Rear Window Heater Relay
Operation of the rear window heater relay is controlled by the CJB, in response to messages received from the ATCM. The ATCM determines operation
of the rear window heater based on information received from the ambient air temperature sensor.
The ATCM (C1629) communicates with the CJB (C0580) via the medium speed CAN bus on YW (high) and YU (low) wires. When energised, the rear
window heater relay (C0585) provides a feed to the rear window heater element (C0381) on an NP wire. The element (C0382) is provided a ground path
on a B wire.
Engine Running
The ATCM monitors engine status via the medium speed CAN bus. The Engine Control Module (ECM) (C0635) provides an engine running signal to
the instrument cluster (C0230) via the high speed CAN bus on YN (high) and YB (low) wires. The instrument cluster (C0230) acts as a gateway and
relays the engine status message to the ATCM (C1629) via the medium speed CAN bus on YU (high) and YW (low) wires.