Seat heater (SIH), function - GF91.30-P-0003LA

MODEL 216.3 as of model year 09/YoM 08 with CODE (873) Heated left and right front seats 

General function requirements 

• C. 15R On

The circuit status is transmitted by the EIS [EZS] control unit (N73) to the following control units via the interior CAN:

• left front seat control unit (N32/1)
• right front seat control unit (N32/2)
• left door control unit (N69/1)
• right door control unit (N69/2)

Seat heaters, general 

Using the seat heater, it is possible to heat the seat cushions and the backrests of the front seats.

The seat heater function consists of the following subfunctions:

• Manual on/off function sequence 
• Automatic switch off function sequence 

Manual on/off function sequence 

The left seat heater is activated via the seat heater switch (S22s12) in the left front seat operation switch group (S22). The right seat heater is activated via the seat heater switch (S23s12) in the right front seat operation switch group (S23).

The seat operation switch group is located in the trim of the respective door.

The request from the left seat heater is read in by the left door control unit via the front door LIN and forwarded to the left front seat control unit via the interior CAN.

The request from the right front seat heater is read in by the right door control unit via the front door LIN and forwarded to the right front seat control unit via the interior CAN.

The left front seat control unit actuates the following heater pads:

• Left front seat heated cushion (R13/1)
• Left front backrest heated cushion (R13/2)

The right front seat control unit actuates the following heater pads:

• Right front seat cushion heater element (R13/3)
• Right front backrest seat cushion heater element (R13/4)

The heat output depends on the heating stage that has been selected using the seat heater switch:

Press once: Heating stage 3 (100 % heat output)

Press two times: Heating stage 2 (60 % heat output)

Press three times: Heating stage 1 (30 % 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 seat heater switch.

When the seat ventilation is activated in vehicles with code (401) Front comfort seats, incl. seat heating and seat ventilation, heating stage 1 of the seat heater is not switched off until the seat ventilation is also switched off.

The selection switch for left or right seat adjustment (S22s10) in the left front seat operation switch group allows operation of the seat heater for the front passenger seat from the driver side. The switchover is active for t = 10 s after pressing the seat adjustment selection switch. This is shown by a light-emitting diode in the left front seat operation switch group.

If the front passenger seat is adjusted within this time, the switchover remains active for a further t = 10 s after the end of the adjustment and is then ended automatically.

The switchover can also be ended by manually pressing the seat adjustment selection switch.

Automatic switch off function sequence 

The timer control is performed by the left front seat control unit or the right front seat 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 parameterized in the left front seat control unit or right front seat control unit using STAR DIAGNOSIS.

Other shutoff criteria:

• Shutoff in the event of a hardware fault

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

• Shutoff after circuit 15R OFF

  If circuit 15C continues to be ON, the timer control continues running for t = 5 min. If circuit 15R is switched on again, then the seat heater is also switched on again at the heating stage activated according to the timer control.

• Shutoff in the event of undervoltage

  In the event of undervoltage, the left front seat control unit or right front seat control unit switches the seat heater off. The timer control continues to run, the light-emitting diodes in the seat heater switch flash.

  There is no automatic reactivation of the seat heater after a shutoff. If the undervoltage persists, it will no longer be possible to switch the seat heater on. The function indicator flashes for t = 0.5 s

  if another request is received.

  The seat heater cannot be switched on again until undervoltage is no longer present.

• Shutoff via on-board electrical system management:

  In order to prevent the battery from discharging in all driving cycle phases, the voltage is monitored continuously. If there is undervoltage in the on-board electrical system, the seat heater may also be deactivated. The timer control continues to run, and the light-emitting diodes in the seat heater switch also stay on.

• Shutoff in the event of overvoltage

  In the event of overvoltage, the left front seat control unit or right front seat control unit switches the seat heater off. The timer control continues to run, the light-emitting diodes in the seat heater switch stay on.

  The seat heater cannot be switched on again until overvoltage is no longer present.

• Shutoff during start-up of engine

  The seat heater is switched off while the engine is started up.

  The timer control continues to run, the light-emitting diodes in the seat heater switch stay on. During the starting procedure, undervoltage is not detected and no flashing due to undervoltage is activated.

• Shutoff during seat adjustment:

  The seat heater is switched off during an active seat adjustment. The timer control continues to run, the light-emitting diodes in the seat heater switch stay on.

• Shutoff during Keyless-Go communication:

  In vehicles with code (889) Keyless-Go, the seat heater is switched off during the Keyless-Go communication.

  The timer control continues to run, the light-emitting diodes in the seat heater switch stay on.

	Seat heater (SIH) location of components		GF91.30-P-0003-02LA
	Electrical function schematic, seat heater (SIH)		PE91.30-P-2050-97CAA
	Seat heater (SIH) block diagram		GF91.30-P-0003-03LA
	Left front seat control unit, component description	N32/1	GF91.29-P-5230LE
	Right front seat control unit, component description	N32/2	GF91.29-P-5240LE
	Left door control unit, component description	N69/1	GF72.29-P-4124LA
	Right door control unit, component description	N69/2	GF72.29-P-4128LA
	Component description for the EZS control unit	N73	GF80.57-P-6003LE