ELECTRICAL
21
DESCRIPTION AND OPERATION The Heated Front Screen (HFS) is a new feature for 2002MY which is available as part of a cold climate pack on
Td5 engine variants only. The HFS system comprises an HFS ECU, an HFS relay, a controlling switch and the
HFS elements.
The HFS comprises two elements laminated in the windscreen. The elements are connected by bus bars within
the screen and therefore the HFS has only one feed and one earth connector.
The HFS is controlled by the HFS ECU which determines when HFS operation is permitted. The ECU also has a
timer which allows HFS operation for up to 8 minutes. The HFS ECU is located behind the instrument pack,
adjacent to the dim/dip relay. The ECU is connected by a multiplug. The ECU receives an ignition feed via the
satellite fuse box and an engine running signal from the engine oil pressure switch.
A non-latching switch for HFS operation is located in the fascia. The switch has a tell-tale lamp to indicate when
the HFS screen is operative.
The HFS relay is located in the under seat fuse box and receives a permanent battery voltage supply via fusible
link 1 in the under seat fuse box. The relay coil is connected to the HFS ECU and an earth point. When the relay is
operated, battery voltage is supplied from the relay, via fuse 25 in the passenger compartment fuse box to the
HFS element.
When the HFS switch is depressed, a momentary earth path is completed from the HFS ECU, through the switch
to earth. This is sensed by the ECU as a request for HFS operation. If the ECU receives an ignition on signal and
an oil pressure signal, it allows HFS operation. The ECU provides an output to the coil of the HFS relay. When the
coil is energised, the contacts close and battery voltage, via fusible link 1 in the under seat fuse box is supplied to
the HFS element, via fuse 25 in the passenger compartment fuse box. The feed is also supplied via a splice joint
to the HFS switch to illuminate the tell tale lamp in the switch.
The HFS ECU will allow screen operation for up to 8 minutes, after which it removes the feed to the HFS relay
coil, which, after the contacts open, removes the supply to the HFS element and simultaneously extinguishing the
tell tale lamp in the switch. If, during the timed operation period, the HFS ECU receives an additional request
signal from operation of the switch, HFS operation is stopped.
When operating, the HFS element draws approximately 25 Amps. To prevent excess drain on the vehicle battery,
if the ignition on signal and/or the oil pressure switch (engine running) signal is lost, the HFS ECU de-energises, if
already operating, or will not energise the HFS relay.
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