Function of rear heated seats - GF91.30-P-0005FQ

MODEL 218 with CODE 872 (Electrically heated left and right rear seats) 

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 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 rear seat heater is operated through the rear seat heater buttons. Pressing the rear seat heater button switches the rear seat heater on and off and also selects the heating stage. The status of each rear seat heater button is read in directly by the corresponding rear door analog/digital converter. The respective rear door analog/digital converter sends this via rear door LIN, rear door control unit and interior CAN to the rear seat heater control unit.

The rear seat heater control unit actuates the following heater pads directly depending on requirements:

• Left rear seat sitting surface heated cushion
• Left rear backrest heated cushion
• Right rear seat sitting surface heated cushion
• Right rear backrest heater pad

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

The rear seat heater control unit sends the status of the seat heater via interior CAN, rear door control unit and the rear door LIN to the corresponding rear door analog/digital converter. The respective rear door analog/digital converter actuates the LEDs in the corresponding rear seat heater button directly.

Pressing once: Heating stage 3 (100 % heat output, three LEDs light up)

Pressing twice: Heating stage 2 (65 % heat output, two LEDs light up)

Pressing three times: Heating stage 1 (35 % heat output, one LED lights up)

Pressing four times: Seat heater is switched off (no LEDs light up)

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

Function sequence for automatic switch off 

The timer control occurs by means of 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 timer control of the three heating levels is adjustable in the rear seat heater control unit using a 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:

  With undervoltage or overvoltage, the rear seat heater control unit switches off the seat heater. The LEDs in the respective rear 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. However, if the shutoff lasts for longer than t = 3 min, the LEDs in the respective rear seat heater button are also switched off. If the seat heater is requested again despite the shutoff, the LEDs in the respective rear seat heater button light up for t = 1.5 s and then go off again.

• Shutoff in the event of a hardware defect:

  If actuation of the heater pads is detected without a current request via a rear seat heater button, the rear seat heater control unit switches the seat heater off.

• Shutoff when the engine starts:

  When the engine is started, the rear seat heater control unit switches off the seat heater. The LEDs in the respective rear seat heater button remain switched on. During the engine start, no undervoltage is recognized and no faults are stored.

• 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.

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

If the PCB temperature reaches T > 110°C, a fault message is stored in the fault memory. Manually switching back on requires cooling of T = 2 °C below the corresponding temperature threshold.

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