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

GF91.30-P-0003FLA Seat Heater, Function
- with CODE (872) Electrically heated left and right rear seats

General function requirements
^ C. 15R On

The circuit 15 status is sent by the electronic ignition lock control unit (N73) over the interior CAN (CAN B) to the rear seat heater control unit (N25/6).

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

The seat heater function is made up of the following subfunctions:
^ Function sequence for manually switching on/off
^ Automatic switch off function sequence

Function sequence for manually switching on/off
The left rear seat heater button (S51/3) and the right rear seat heater button (S51/4) switch the rear seat heater on and off while also regulating heater output.

Actuation of the left rear seat heater button is read in by the left rear door analog/digital converter (N69/16) and sent over the left rear door LIN (LIN B9) to the left rear door control unit (N69/3). Actuation of the right rear seat heater button is read in by the right rear door analog/digital converter (N69/17) and sent over the right rear door LIN (LIN B10) to the right rear door control unit (N69/4). The corresponding rear door control unit sends the request over the interior CAN to the rear seat heater control unit, which then switches on the seat heater.

The following heater pads are actuated by the rear seat heater control unit as and when required:
- Left rear seat surface heater pad (R13/5)
- Left rear backrest heater pad (R13/6)
- Right rear seat surface heater pad (R13/7)
- Right rear backrest heater pad (R13/8)

Heat output is dependent on the heater stage selected by means of each rear seat heater button. The function indication for the activated heater stage is effected through three red LEDs in each rear seat heater button.

Press once: Heating stage 3 (100 % heat output, three LEDs illuminated)
Press two times: Heating stage 2 (65 % heat output, two LEDs illuminated)
Press three times: Heating stage 1 (35 % heat output, one LED illuminated)
Press four times: Seat heater switched off (no LED illuminated)

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

Automatic switch off function sequence
The timer control is realized in the rear seat 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.
The seat heater is then automatically switched off.

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

Other shutoff criteria:
- Shutoff after circuit 15R Off:
If circuit 15C is still On, the timer control continues to run for 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:
If the rear SAM control unit with fuse and relay module (N10/2) switches off the seat heater, the LEDs remain initially switched on.

If the on-board electrical system reaches its normal voltage within the next t = 3 min., the seat heater function is automatically reactivated.

If the shutoff lasts longer than t = 3 min, the LEDs are also switched off.

If shutoff continues and the function is requested again by pressing the button, the LEDs light up for t = 1.5 s and then go out.

- Shutoff in the event of a hardware fault
If heater pad actuation is detected without a currently existing switch-on request or function condition, the seat heater is switched off.

- Shutoff for overtemperature of PCB in rear seat heater control unit
- 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 PCB temperature T > 110 °C the seat heater can no longer be activated.

If the PCB temperature reaches T > 110 °C, a fault message is stored in the fault memory. Manual switch on requires a cooling down of T = 2 °C for the corresponding temperature threshold.

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