Seat Heater, Function - GF91.30-P-0003RF
Model 205, 253
with code 401 (Climatised front seats)
Model 205, 253
with code 872 (Left and right rear seat heating)
Model 205, 253
with code 873 (Left and right driver's seat heating)
Driver's seat heating
Front passenger seat heating
Model 205, 253
as of model year 2016
with code 401 (Climatised front seats)
except code 221 (Electrically adjustable left driver seat)
except code 222 (Electrically adjustable right driver seat)
except code 242 (Front passenger seat, electrically adjustable with
memory function)
except code 275 (Memory Package (driver's seat, steering column
and mirror))
Model 205, 253
as of model year 2016
with code 873 (Left and right driver's seat heating)
except code 221 (Electrically adjustable left driver seat)
except code 222 (Electrically adjustable right driver seat)
except code 242 (Front passenger seat, electrically adjustable with
memory function)
except code 275 (Memory Package (driver's seat, steering column
and mirror))
The front seat heater control unit in the front passenger seat functionally replaces the driver seat heater control unit and the front passenger seat heater control unit. In the following information, only the term "seat heater control unit" is used.
Rear seat heating, shown with code 872 (Seat heating in rear)
Function requirements, general
- Circuit 15R ON or circuit 15 ON
The electronic ignition lock control unit sends the status of circuit 15 via the interior CAN to the rear SAM control unit.
Seat heater (SIH), general
The seat heater heats the seat cushions and seat backrests of the seats in three heating stages. The master control unit of the seat heater is the rear SAM control unit.
For model 205 with code 577 (Remote activation of heating and ventilation systems) and for plug-in hybrid vehicles, the driver's seat heater can be switched on using the auxiliary climate control for a maximum of 60 s (after unlocking the vehicle). The driver's seat is thus prewarmed before departure.
Seat heater activation/deactivation
The seat heater is operated using the front seat heating switch in the respective seat climate control switch group or via the respective rear seat heater button. The left front door control unit reads in the status of the left front seat heater switch over the left front door LIN and sends it over the interior CAN to the rear SAM control unit. The right front door control unit reads in the status of the right front seat heater switch via the right front door LIN, and sends it via the interior CAN to the rear SAM control unit.
For model 253 as of model year 2020, the seat heater can also be activated/deactivated via the voice control system (VCS). The head unit transmits in this case the relevant request via the user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit.
The heating output of the seat heater can be set in three heating stages. Heating stage 3 is active when the seat heater is initially activated.
- Heating stage 3: 3 LEDs are illuminated in the seat heating switch.
The seat heater is operated at 100 %.
- Heating stage 2: 2 LEDs are illuminated in the seat heating switch.
The seat heater is operated at 65 %.
- Heating level 1: 1 LED is illuminated in the seat heating switch. The seat heater is operated at 35 % output.
If the front seat heating switch or the rear seat heater button is actuated again for the same terminal status, only 90 % of the heating output is provided for heating stage 3. The heating output of the respective heating stage can be set at the factory using the diagnostic tester.
Driver's seat heater:
The rear SAM control unit evaluates the incoming request and transmits this in an equipment-dependent manner via one of the following connections:
- Via interior CAN to the driver seat control unit (with CODE 275 (Memory package))
- Over the heater LIN to the driver seat control unit (with CODE 221 (Left electrically adjustable driver seat))
- Via the heater LIN to the seat heater control unit (except code 275 (Memory package) and except code 221 (Left electrically adjustable driver seat))
The driver seat control unit or the seat heater control unit then actuates the following heater pads directly:
- Left front seat cushion heater pad
- Left front seat backrest heater pad
- Heater pad for adjustable seat cushion length, left front seat (with CODE 275 (Memory package) or CODE 221 (Left electrically adjustable driver seat))
The driver seat control unit or the seat heater control unit continuously checks the function of all seat heater components involved and sends the corresponding status via one of the following connections, depending on the equipment:
- Via heater LIN to the rear SAM control unit (except CODE 275 (Memory package))
- Via interior CAN to the rear SAM control unit (with CODE 275 (Memory package))
The rear SAM control unit sends the seat heater status over the interior CAN, left front door control unit and left front door LIN to the front left climate control switch group that accordingly actuates the LEDs in the front left seat heating switch.
Front passenger seat heater:
The rear SAM control unit evaluates the incoming request and transmits this in an equipment-dependent manner via one of the following connections:
- Over the interior CAN to the front passenger seat control unit (with CODE 242 (Electrically adjustable front passenger seat with memory function))
- Over the heater LIN to the front passenger seat control unit (with CODE 222 (Electrically adjustable right front seat))
- Via the heater LIN to the seat heater control unit (except code 242 (Electrically adjustable front passenger seat with memory function) and except code 222 (Right electrically adjustable front seat))
The front passenger seat control unit or the seat heater control unit then actuates the following heater pads directly:
- Right front seat cushion heater pad
- Right front seat backrest heater pad
- Heater pad for adjustable seat cushion length, right front seat (with CODE 242 (Electrically adjustable front passenger seat with memory function) or CODE 222 (Electrically adjustable right front seat))
The front passenger seat control unit or the seat heater control unit continuously checks the function of all seat heater components involved and sends the corresponding status via one of the following connections, depending on the equipment:
- Over the heater LIN to the rear SAM control unit (except CODE 242 (Electrically adjustable front passenger seat with memory function))
- Over the interior CAN to the rear SAM control unit (with CODE 242 (Electrically adjustable front passenger seat with memory function))
The rear SAM control unit sends the seat heater status over the interior CAN, right front door control unit and right front door LIN to the front right seat climate control switch group that accordingly actuates the LEDs in the front right seat heating switch.
Rear seat heater (with code 872 (Seat heating in rear)):
The left rear door control unit or the right rear door control unit reads in the status of the respective rear seat heater button via the door LIN and sends this via the interior CAN to the rear SAM control unit. The rear SAM control unit evaluates this and sends the corresponding request via the heater LIN to the rear seat heater control unit. The rear seat heater control unit then actuates the following heater pads directly:
- Left rear seat:
- Left rear seat sitting surface heated cushion
- Left rear backrest heated cushion
- Right rear seat:
- Right rear seat sitting surface heated cushion
- Right rear backrest heater pad
The rear seat heater control unit continuously checks the operative function of all involved components of the seat heater and sends the corresponding status via the heater LIN to the rear SAM control unit. According to the frequency with which the respective rear seat heater button is pressed, the rear SAM control unit sends the status of the seat heater via the interior CAN, rear door control unit, and rear door LIN to the rear seat heater button. The LEDs in the rear seat heater button are actuated accordingly.
Switch seat heater off automatically
Then the seat heater is automatically switched off (timed). The timer control is stored in the rear SAM control unit.
- Heating level 3 is active for 8 mins. Then the system automatically switches to heating stage 2.
- Heating level 2 is active for 10 mins. Then the system automatically switches to heating level 1.
- Heating level 1 is active for 20 mins. Then the seat heater is automatically switched off.
Other shutoff criteria:
- Shut-off in the event of a hardware defect
If the seat heater is actuated without a corresponding request, the rear SAM control unit accordingly requests the deactivation of the power supply of the seat heater. The power supply of the seat heater is then deactivated by the respective seat heating control unit, the driver's seat control unit or the front passenger seat control unit.
- Deactivation in event of excess temperature of PCBs in respective control unit
- At a printed circuit board temperature of more than 70°, heating level 3 can no longer be activated.
- At a printed circuit board temperature of more than 80°, heating level 3 and heating level 2 can no longer be activated.
- At a printed circuit board temperature of more than 90°, the seat heater can no longer be activated.
If no PCB temperature value is available, the interior temperature value is accordingly evaluated as an alternative. The climate control control unit sends the interior temperature value via the interior CAN to the rear SAM control unit.
If the printed circuit board temperature reaches 90°, a fault message is stored in the fault memory. Manually switching back on requires cooling of 2° below the corresponding temperature threshold.
- Shutoff in the event of an error (short circuit, overload or open circuit (line break))
The respective control unit detects a possible short circuit, overload or a line break of the actuated heater pad and deactivates the power supply. The listed fault sources can be individually diagnosed for each heater pad using the diagnostic tester.
- Shutoff when the engine starts
In the case of an engine start (cold start), the seat heater is deactivated for 20 s. In the case of a warm start, the seat heater is deactivated for 3 to 5s. The timer control continues to run, and the LEDs remain switched on. The voltage drop during the engine starting procedure is not evaluated as undervoltage.
- Switching off by means of energy management
In order to prevent the battery from discharging in all driving cycle phases, the state of charge is continuously evaluated. Depending on the situation, the HS [SIH] are also deactivated.
If the seat heater is deactivated, the LEDs initially remain activated. If the on-board electrical system voltage is stabilized within the next 3 minutes to the normal voltage, the seat heater restarts automatically. However, if the deactivation lasts longer than 3 min, the LEDs are also deactivated. If the deactivation persists and the function is requested again, the LEDs are illuminated for 1.5 s and then go out.
- Switch off in event of voltage drop
In the case of the failure of one of the two power supply lines of the respective control unit, the seat heater is deactivated.
- Shutoff after circuit 15R OFF
At circuit 15R OFF and circuit 15C ON, the timer control runs on for 5 minutes. If circuit 15R is switched on again, the seat heater is also switched on again.
- Shut-off in the event of "Timeout error"
If the request of the rear SAM control unit for actuating the seat ventilation is discontinued or a "Timeout period" from the electronic ignition lock control unit is recognized, the seat heater is switched off.
- Shutoff at end of diagnosis
The seat heater is deactivated at the end of a diagnosis.
| Electrical function schematic, seat heater, rear seats | Model 205, 253 with code 872 (Left and right rear seat heating) | PE91.30-P-2055-97FBA | |
| Electrical function schematic, seat heater, front | Model 205, 253 with code 401 (Climatised front seats) Model 205, 253 with code 873 (Left and right driver's seat heating) | PE91.30-P-2056-97FBA | |
| Overview of system components of comfort heating systems | GF91.30-P-9990RF |