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Electrically heated rear window and door mirrors

Electrically heated rear window and door mirrors

A number of heating wires are fastened to the inside of the rear window glass. On the Saab 9-5 4D these heating wires also serve as an antenna for the audio system in combination with an antenna amplifier.

The glass in the door mirrors also has heating conductors.

On cars with ACC the electrical heating is automatically engaged and disengaged from the ACC control module or manually from the switch on the ACC panel. The ACC control module then sends a bus message which is used by DICE to activate the relay for the electrical heating. When DICE has activated the relay it sends a bus message back to the ACC which lights a symbol on the display.

The time for which the electrical heating is engaged depends on the outside temperature or it can be switched off manually. Activation time is as follows:


• 30°C = 0 minutes

• 0°C = 9 minutes

• -40°C = 12 minutes


DICE controls the battery voltage after 3, 6 and 9 minutes. If the voltage falls below 12.6V or rises above 16V then DICE switches off the electrical heating.


To avoid putting a greater load on the battery than necessary when the starter motor is activated (+15 ON, +54 OFF), the DICE turns off the electric heating. When the ignition switch subsequently returns from START to ON, the DICE turns on the electric heating again. For reasons of safety, turn-off time is limited to 20 seconds so that electric heating will be functional even in the event of a fault, i.e. if no +54 current is present.


Combined electrically heated rear window and antenna 4D


The heating conductors in the rear window are also used as an antenna for the audio system in combination with an antenna amplifier.

The conductors in the rear window are grounded via an antenna filter (coil) to the car's bodywork. The resistance of the antenna filter (coil) is very low so there is no appreciable affect on the current flowing through it. The antenna filter (coil) is, however, a hinder to the high-frequency radio waves picked up by the conductors (antenna) and prevents them form grounding to the bodywork. There is a similar function built into the antenna amplifier that prevents radio waves from entering the car's wiring.

The antenna filter is located on the left-hand C pillar.

Cars with ACC


When the ignition is ON, +15 current is fed from fuse 26 to relay 113. The ACC control module outputs a message on the bus to the DICE control module 628 when it requests activation (automatically or when the switch on the ACC panel is pressed). DICE then grounds the coil in relay 113 via pin 52. +30 current is then fed from fuse 18 via the relay contacts and the antenna amplifier 624 to the electrically heated rear window 115, which is grounded through the antenna filter 644.

At the same time current is supplied from relay 113 to the heating elements in rear-view mirrors 207D/P where the left-hand side rear-view is grounded in grounding point G33 and the right-hand side rear-view mirror is grounded in grounding point G24.

When the relay has been activated, DICE outputs a message on the bus to ACC which turns on the indicator light on its display.


Electric heating uses the following information

Information Sensor system
Relay, activation

DICE

The relay turns on the heating.

Relay, inactivation

DICE

The relay turns off the heating.