Heated Rear Seat

Heated Rear Seat

Rear seat heating is available as an option in the Saab 9-5. The rear seat is then fitted with two heating pads, one in each 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 exterior temperature.

Description of operation
When the switch (252R) for the heated rear seat is pressed, B+ is supplied to pin 9 in TWICE. TWICE grounds the relay for the heated rear seat via pin 52. The relay trips and supplies B+ via fuse 10 to the heating pad in the rear seat and to the display switch.

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









When the exterior temperature exceeds -5°C, the heating is connected for 3 minutes. If the exterior temperature is less than -5°C, the activation time is longer. At -14°C, the activation time has reached a maximum. This time is programmable between 3 and 18 minutes, but is normally preset at 10 minutes.

To avoid loading the battery more than necessary when the starter is activated (+15 ON, +54 OFF), TWICE switches off the electric heating. When the ignition key is then turned back from ST to ON, TWICE turns the heating on again.

For safety reasons, the disconnection time is maximized 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.

Controls and 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 cigar lighter. For further information see Group 3 DICE, Controls and 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
^ Shorting to battery positive (B+).

No diagnostic trouble code is generated for a voltage below 11 V or on diagnostic communication. The control module output can be activated using the diagnostic tool.