GF91.30-P-0003RC Seat Heater (SIH), Function

GF91.30-P-0003RC Seat Heater (SIH), Function
- with CODE (873) Left and right front seat heaters

General function requirements
^ C. 15R On

The circuit 15 status is sent by the EIS [EZS] unit (N73) over the interior CAN to the SH [SIH], AIRSCARF and steering wheel heater control unit (N25/7).

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

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

Manual on/off function sequence
Pressing the left SH [SIH] switch (N72/1s10) or the right SH [SIH] switch (N72/1s11) in the upper control panel control unit (N72/1) requests the SH [SIH] function.

The upper control panel control unit reads in the status of the SH [SIH] switch and sends it over the interior CAN to the SH [SIH] control unit. The SH [SIH] control unit then actuates the following components in accordance with the relevant request:
- Left front seat heated cushion (R13/1)
- Left front backrest heated cushion (R13/2)
- Right front seat cushion heater element (R13/3)
- Right front backrest seat cushion heater element (R13/4)

The actuation frequency for the SH [SIH] switch determines the heat output of the SH [SIH]:
Press once: Heating stage 3 (100 % heat output)
Press two times: Heating stage 2 (70 % heat output)
Press three times: Heating stage 1 (40 % heat output)
Operate four times: Seat heater is switched off

The particular heating stage that is active is indicated via red LEDs in the corresponding SH [SIH] switch.

If, at circuit 15, the SH [SIH] is selected again, heating stage 3 is provided with only 90 % of the heat output.

Automatic switch off function sequence
The SH [SIH] duration is regulated by the SH [SIH], AIRSCARF and steering wheel heater control unit:
- Heating stage 3 is active for t = 5 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 heater stages can be parameterized through STAR DIAGNOSIS in the SH [SIH] control unit.

Other shutoff criteria:
- Switch off after circuit 15R OFF:
For a circuit 15C ON status the timer control continues for the period of t = 5 min. If circuit 15R is switched on again, then the SH [SIH] is also activated at the heating stage in line with the timer control.

- Switch off at undervoltage or overvoltage:
In the event of undervoltage or overvoltage, the SH [SIH] control unit switches off the SH [SIH]. The timer control continues to run. At undervoltage the light emitting diodes flash on and off at 1.5 Hz and 50 % brightness. At overvoltage the light emitting diodes are permanently on.

The SH [SIH] can only be switched on again when a permissible voltage is applied.

- Switch off during engine starting process:
When the engine is started, the SH [SIH] control unit switches off the SH [SIH]. The timer control continues to run, and the light emitting diodes remain on.

During the starting procedure an undervoltage will not be recognized.

- Switch off during overtemperature.
- Heating stage 3 can no longer be activated if the interior temperature is T > 42 °C.
- Heating stage 3 and heating stage 2 can no longer be activated if the interior temperature is T > 45 °C.

- The SH [SIH] can no longer be activated at an interior temperature of T > 55 °C.

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

- Switch off for hardware defect:
If the SH [SIH] control unit detects an actuation of the heater pads without a currently pending switch-on request or function condition, it switches off the SH [SIH].