Seat heater (SIH), function - GF91.30-P-0003LE
MODEL 221.0 /1 as of model year 09/YoM 08 with CODE (873) Heated left and right front seats with CODE (401) Front comfort seats, incl. seat heating and seat ventilation with CODE (872) Electric seat heater for left and right rear seats with CODE (402) Rear comfort seats, incl. seat heating and seat ventilation
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:
- rear seat control unit (N25/6)
- left front seat control unit (N32/1)
- right front seat control unit (N32/2)
- left front door control unit (N69/1)
- right front door control unit (N69/2)
- left rear door control unit (N69/3)
- right rear door control unit (N69/4)
Seat heaters, general
Using the seat heater, it is possible to heat the seat cushions and the backrests of the front seats and the rear outer 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 front seat heater is activated via the seat heater switch (S22s12) in the left front seat operation switch group (S22). The right front 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 respective trim of the front door.
The request from the left front seat heater is read in by the left front 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 front 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 left rear outer seat heater is activated via the seat heater switch (S55/1s12) in the left rear seat operation switch group (S55/1).
The right rear outer seat heater is activated via the seat heater switch (S55/2s12) in the right rear seat operation switch group (S55/2).
The request from the left rear seat heater is read in by the left rear door control unit via the rear door LIN and forwarded to the rear seat control unit via the interior CAN.
The request from the right rear seat heater is read in by the right rear door control unit via the rear door LIN and forwarded to the rear seat control unit via the interior CAN.
The rear seat control unit actuates the following heater pads:
- Left rear seat heated cushion (R13/5)
- Left rear backrest heated cushion (R13/6)
- Right rear seat heated cushion (R13/7)
- Right rear backrest heated cushion (R13/8)
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 front seat control units and by the rear 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 of the three heating stages can be parameterized in the front seat control units and rear 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 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 front seat control units and the rear seat control unit switch 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-0003-02LE | ||
| Electrical function schematic, seat heater (SIH) | With code (873) Heated left and right front seats or code (401) Front comfort seats, incl. seat heating and seat ventilation: | PE91.30-P-2050-97SAA | |
| Electrical function schematic, seat heater (SIH) | With code (872) Electric seat heater for left and right rear seats or code (402) Rear comfort seats, incl. seat heating and seat ventilation | PE91.30-P-2050-97SAB | |
| Seat heater (SIH) block diagram | GF91.30-P-0003-03LE | ||
| Rear seats control unit, component description | N25/6 | GF91.29-P-5250LE | |
| 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 front door control unit, component description | N69/1 | GF72.29-P-4141LE | |
| Right front door control unit, component description | N69/2 | GF72.29-P-4142LE | |
| Rear door control unit, component description | N69/3, N69/4 | GF72.29-P-6020LE | |
| Component description for the EZS control unit | N73 | GF80.57-P-6003LE |