Function Of Rear Heated Seats - GF91.30-P-0005GR

MODEL 166 up to model year 2016 with CODE 872 (Electrically heated left and right rear seats) 

Function requirements, general 

• Circuit 15R ON

The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the RCP [HBF] control unit.

Seat heaters, general 

The seat heater enables the seat cushions and seat backrests of the rear seats to be heated in three heating levels.

The seat heater function encompasses the following subfunctions:

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

Function sequence for manually switching on/off 

The left rear seat heater button and the right rear seat heater button switch the rear seat heater on or off while also regulating heater output.

The actuation of the left rear seat heater button and the right rear seat heater button is read in directly by the RCP [HBF] control unit.

The corresponding RCP [HBF] control unit sends the request over the interior CAN to the rear seat heater control unit, which then switches on the corresponding seat heater.

The following heater pads are actuated by the rear control unit as and when required:

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

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

• 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 rear control unit is responsible for the timer control:

• Heating stage 3 is active for t = 5 min.

  Then the system automatically switches to heating stage 2.

• Heating level 2 is active for t = 10 min.

  Then the system automatically switches to heating level 1.

• Heating level 1 is active for t = 20 min.

  The seat heater is then automatically switched off.

The time settings for the three heating levels can be adjusted in the rear control unit using the diagnostic tester.

Other shutoff criteria:

• Shutoff after circuit 15R OFF:

  If circuit 15C remains ON, the timer control runs on 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.

• Deactivation with undervoltage or overvoltage:

  If the rear control unit switches the seat heater off, the LEDs in the corresponding rear seat heaters button remain switched on for the time being.

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

  However, if the shutoff lasts longer than t = 3 min, the LEDs in the corresponding rear seat heater button are also switched off. If shutoff continues and the function is requested again by pressing the rear seat heater button, the LEDs in the corresponding rear seat heater button light up for t = 1.5 s and then go out.

• Shutoff in the event of a hardware defect:

  If heater pad actuation is detected without a current existing switch-on request or function condition, the seat heater is switched off.

• Shutoff for overtemperature of PCB in rear 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. To be able to switch the seat heater back on again manually, the PCB temperature must have dropped by T = 2 °C below the corresponding temperature threshold.

• Shutting off during the engine starting procedure.

  The timer control continues to run and the LEDs remain on. No undervoltage is detected during startup.

	Electrical function schematic, seat heater, rear seats		PE91.30-P-2055-97NAA
	Overview of system components of comfort heating systems		GF91.30-P-9990GR