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Electrically heated rear seat

Electrically heated rear seat




Electric heating of the rear seat is available as an option on the Saab 9-3. The rear seat is then fitted with two heating pads, one on each side of the seat.

The heating is controlled manually and can only be turned on when the ignition is ON. The heating time is controlled by TWICE and depends on the outdoor temperature.

Description of operation


When the switch (503) for the electrically heated rear seat is pressed, B+ is fed to pin 9 on TWICE. TWICE grounds the relay (511) for the electrically heated rear seat via pin 52.

The relay trips and supplies B+ via fuse 33 to the heating pads in the rear seat and to the indicator in the switch.

The heating time depends on the outdoor temperature. TWICE receives information on the outdoor temperature from SID via the bus.

When the outdoor temperature exceeds -5°C, the heating is connected for 5 minutes. If the outdoor temperature is lower than -5°C, the activation time is longer. At -14°C, the activation time has reached a maximum. The time is programmable between 3 and 18 minutes, but is normally preset at 8 minutes.



So that the battery is not drained unnecessarily when the starter motor is cranking (+15 ON, +54 OFF), TWICE turns off the heating. When the ignition key then returns from ST to ON, TWICE turns on the heating again.

For safety reasons, the disconnection time is maximised at 20 seconds so that the heating works even if +54 is missing in the event of a fault.

TWICE receives information on the ignition +54 from DICE via the bus. Ignition +15 is connected to pin 16 of TWICE.

Button and controls lighting

The switch for the heated rear seat is lit by a bulb powered from DICE (pin 49, rheostat level). This voltage supplies the buttons and controls, ashtray light and cigarette lighter. For further information see Group 3 DICE, Button and controls lighting.

Diagnostics

In the event of a fault in the relay control circuit, diagnostic trouble code B1130 is generated in TWICE. The diagnostic trouble code is generated on:


• Open circuit or short circuit to ground

• Short-circuit to B+


The diagnostic trouble code is not generated when the voltage is below 11V or during diagnostic communication. The control module output can be activated with the diagnostic tool.