Heated Rear Window (HRW)

HEATED REAR WINDOW (HRW)

DESCRIPTION

General
Operation of the Heated Rear Window (HRW) is continued by the Automatic Temperature Control (ATC) ECU via the non latching HRW switch. After 10 minutes of operation, (when ambient temperature is -15 °C (50 °F) or above) or 17 minutes (when ambient temperature is less than -15 °C (50 °F)), the ATC ECU operates the HRW at low power for 60 minutes. During the 60 minutes, the ATC ECU cycles the HRW relay off for 80 seconds and on for 40 seconds. If the HRW switch is pressed again during the low power phase, the ATC ECU returns the HRW to full power by keeping the HRW relay energised for 5 minutes. At the end of the 5 minutes the low power phase is repeated.

The ATC ECU outputs a K bus message when the HRW is active. The message allows the navigation computer to compensate for the effect of the magnetic field generated when the HRW is active. The BCU transfers the message onto the P bus for the door modules, which activate the door mirror heaters together with the HRW.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 5 and fuse 53 of the passenger compartment fuse box (C0632) on an R wire. Fusible link 5 (C0588) is connected to fuse 9 of the rear fuse box (C2024) by an R wire. Fuse 9 provides a constant battery feed to the HRW relay, which is also located in the rear fuse box.

Fuse 53 of the passenger compartment fuse box (C0583) provides a constant battery feed to the ignition switch (C0028 on V8 vehicles) on an R wire. When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0028 on V8 vehicles) to fuse 2 of the passenger compartment fuse box (C0585) on a G wire. Fuse 2 (C0587) provides an ignition feed to the HRW relay coil (C2022) on a GY wire. The earth path for the relay coil (C2022) is controlled by the ATC ECU (C1629) on a UN wire.

HRW
When the HRW switch is pressed, a momentary earth path (C1630) is created on an N wire. If all operational conditions are met (see 'Description' above), the ATC ECU energises the HRW relay. The energised HRW relay (C2021) provides a feed to the HRW (C0381) on a B wire. The HRW (C0382) is earthed on an N wire.