Front heated seats function - GF91.30-P-0004FQ

MODEL 218 with CODE 401 (Front deluxe seats, incl. seat heating and seat ventilation)

MODEL 218 with CODE 873 (Heated left and right front seats)

Fig 1: Front Heated Seats - Block Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general

Circuit 15R ON

The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the front SAM control unit and the rear SAM control unit.

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 SIH function includes the following subfunctions:

Function sequence for manually switching on/off
Function sequence for automatic switch off

Function sequence for manually switching on/off

The operation of the seat heater occurred via the front seat heater buttons in the upper control panel control unit. The upper control panel control unit reads in the status of the respective front seat heater button directly and sends this to the rear SAM control unit via the instrument panel LIN, front SAM control unit and interior CAN.

The rear SAM control unit actuates the following heater pads according to the request:

Left front seat sitting surface heated cushion
Left front backrest heated cushion
Right front seat sitting surface heated cushion
Right front backrest heated cushion

The heat output depends on the selected heating level. The respective active heating level is shown via red LEDs in the corresponding front seat heater button.

Pressing once: Heating stage 3 (100 % heat output, three LEDs light up)
Press twice: heating level 2 (70 % heat output, two LEDs light up)
Press three times: heating level 1 (40 % heat output, one LED lights up)
Pressing four times: Seat heater is switched off (no LEDs light up)

The rear SAM control unit sends the status of the seat heater via interior CAN, front SAM control unit and instrument panel LIN to the upper control panel control unit. The upper control panel control unit actuates the LED in the respective front seat heater button directly.

If the seat heater is selected again with the same circuit status, heating stage 3 is provided with only 90 % of the heat output.

Vehicle with code (401) Front comfort seats, incl. seat heating and seat ventilation:

The rear SAM control unit only switches off heating level 1 of the seat heater with the seat ventilation activated when the seat ventilation is also switched off.

Function sequence for automatic switch off

The timer control is performed 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 of the three heating levels can be set using the diagnostic tester.

Other shutoff criteria:

Shutoff after circuit 15R OFF:
With circuit 15R OFF and circuit 15C ON, the timer control runs on for another t = 5 min. If circuit 15R is switched on again, the seat heater is also switched on again.
Deactivation with undervoltage or overvoltage:
In the event of undervoltage or overvoltage, the rear SAM control unit switches off the seat heater. The LEDs in the respective front seat heater button initially remain switched on. If the on-board electrical system voltage is stabilized again within a period of t = 3 min, the seat heater starts again automatically. If deactivation lasts longer than t = 3 min, however, the LEDs in the respective front seat heater button are also switched off. If the seat heater is requested again despite shutoff, the LEDs in the respective front seat heater button light up for t = 1.5 s and then going out again.
Shutoff in the event of a hardware defect:
If actuation of the heater pads without a current request via a front seat heater button is recognized, the rear SAM control unit switches off the seat heater.
Shutoff when the engine starts:
During engine start, the rear SAM control unit switches the seat heater off. The LEDs in the respective front seat heater button remain switched on. During the engine start, no undervoltage is recognized and no faults are stored.
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.

The seat heater can no longer be activated if the PCB temperature is T > 110 °C.

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

	Electrical function schematic, seat heater (SIH)		PE91.30-P-2050-97XAA
	Overview of system components of comfort heating systems		GF91.30-P-9990FQ