GF91.30-P-0003CA Seat Heater, Function

GF91.30-P-0003CA Seat Heater, Function
- with CODE (873) Heated left and right front seats
- with CODE (401) Front comfort seats, including seat heating and seat ventilation

General function requirements
^ Circuit 15R ON

The electronic ignition lock control unit (N73) sends the circuit 15 status to the interior CAN (CAN B).

Seat heater (SIH), general
Using the SIH, it is possible to heat the seat cushions and the backrests of the front seats in three heating stages.

The seat heater function is made up of the following subfunctions:
^ Manual on/off function sequence
^ Automatic switch off function sequence

Manual on/off function sequence
Operation takes place via the left front heated seat button
(N72/1s10) and the right front heated seat button (N72/1s11) in the upper control panel control unit (N72/1).

Seat heater button requests are read in by the upper control panel control unit and sent over the instrument panel LIN (LIN 1) to the front SAM control unit with fuse and relay module (N10/1). This routes the requests to the rear SAM control unit with fuse and relay module (N10/2) via the CAN interior compartment.

The following heater pads are actuated by the rear SAM control unit as requested:
- Left front seat sitting surface heated cushion (R13/1)
- Left front backrest heated cushion (R13/2)
- Right front seat sitting surface heated cushion (R13/3)
- Right front backrest heated cushion (R13/4)

The heat output is dependent on the heating stage chosen on the seat heater button and each activated heating stage is indicated by red LEDs in the corresponding seat heater button:
Press once: Heating stage 3 (100 % heating output, three LEDs illuminated)
Press two times: Heating stage 2 (70 % heating output, two LEDs illuminated)
Press three times: Heating stage 1 (40 % heating output, one LED illuminated)
Press four times: Seat heater switched off (no LED illuminated)

If the seat heater is selected again with the same circuit status, heating stage 3 is provided with only 90 % of the heat output. When the seat ventilation is activated in vehicles with code (401) Front comfort seats, incl. seat heating and seat ventilation, heating stage 1 of the seat heater is not switched off until the seat ventilation is also switched off.

Automatic switch off function sequence
The timer control is realized by the rear SAM control unit.
- Heating stage 3 is active for t = 8 min.
Then the system automatically switches to heating stage 2.

- Heating stage 2 is active for t = 10 min.
Then the system automatically switches to heating stage 1.

- Heating stage 1 is active for t = 20 min.
Then the SIH is automatically switched off.

The time settings for the three heating stages can be adjusted in the rear SAM control unit via the diagnostic tester.

Other shutoff criteria:
- Shutoff after circuit 15R OFF
If circuit 15C continues to be ON, the timer control continues running for t = 5 min. If circuit 15R is switched on again, then the seat heater is also activated at the heating stage in line with the timer control.

- Switching of with undervoltage and overvoltage:
If the rear SAM control unit switches off, the LED in the corresponding front seat heater button initially remains on. If the on-board electrical system reaches its normal voltage within the next t = 3 min., the seat heater function is automatically reactivated.

However, if the shutoff lasts longer than t = 3 min., the LED in the front seat heater button is also switched off.

It the shutoff procedure continues and the function is requested again for the corresponding front seat heater button, the LED comes on for t = 1.5 s and then goes out.

- Switching off in the event of defective hardware:
If an actuation of the heater pads by the seat heater button is detected without any request pending, the power supply for the seat heater is switched off.

- Shutting off when starting engine:
The timer control continues to run and the LEDs remain on. No undervoltage is detected during startup.

- Switching off if temperature of printed circuit boards in the rear SAM control unit is too high
- Heating stage 3 can no longer be activated if the PCB temperature is T > 90 °C.
- Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is T > 100 °C.
- At a printed circuit board temperature T > 110 °C the seat heater can no longer be activated.

If no plausible circuit board temperature value is present, the outside temperature value is used instead.