Front Heated Seats Function - GF91.30-P-0004FR
Model 257, 290
up to model year 2021
with code 401 (Climatised front seats)
Model 257, 290
up to model year 2021
with code 873 (Left and right driver's seat heating)
Model 257, 290
up to model year 2021
with code 902 (Seat heater Plus for driver and front passenger)
With code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heating for driver and front passenger), except code 275 (Memory Package) and except code 278 (Fully electric front seats)
With code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heating for driver and front passenger) and code 275 (Memory Package) or code 278 (Fully electric front seats)
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.
Front seat heater, general
The seat heater enables the seat cushions and backrests to be heated in three heating levels. The master control unit for the seat heater function is the rear SAM control unit.
The seat heater at the front passenger side can also be operated via the left front seat climate control switch group.
Model 257, 290 up to model year 2021
with code 902 (Seat heater Plus for driver and front passenger)
The heater pads are energized stronger than in a normal case depending on the interior temperature. This enables faster heating to be achieved. The lower the interior temperature, the faster the heater pads are heated up. The climate control control unit sends the interior temperature value via the interior CAN to the rear SAM control unit.
The front seat heater function includes the following subfunctions:
- Switch seat heating on and off
- Driver's seat heating
- Front passenger seat heating
- Hot stone (with code 902 (Seat heating Plus for driver and front passenger) and code 432 (Left and right dynamic multicontour seat))
- Switching off automatically
Switch seat heating on and off
The seat heater switch in the respective seat climate control switch group switches the seat heater on and off as well as regulating the heat output (seat heater deactivated in initial condition, all LEDs off):
- Press one time: 3 LEDs light up, heating level 3 of the seat heating is activated (100 % heat output).
- Press twice: 2 LEDs light up, heating level 2 of the seat heating is activated (65 % heating output).
- Press three times: 1 LED lights up, heating level 1 of the seat heating is activated (35 % heating output).
- Press four times: All LEDs off, seat heater switched off
If the seat heating is selected again with the same circuit status, only 90 % heating output is available for heating level 3. The heating output of the individual heating levels can be adjusted ex-factory through a diagnosis tester.
Function note
The seat heater is switched off automatically at a set time. The timer control is realized by the rear SAM control unit.
- Heating level 3 is active for 8 minutes. Then the system automatically switches to heating stage 2.
- Heating level 2 is active for 10 minutes. Then the system automatically switches to heating level 1.
- Heating level 1 is active for 20 minutes. The seat heater is then automatically switched off.
The timer control of the three heating stages can be adjusted in the factory using a diagnostic tester.
Driver's seat heating
The left front door control unit reads in the status of the left front seat heater switch via the left front door LIN and sends a matching request via the interior CAN to the rear SAM control unit. The rear SAM control unit evaluates this and sends the request to switch on the seat heating, depending on the equipment involved, over the following connection:
Vehicles with code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger)
- Except code 278 (Fully electric front seats) and except code 275 (Memory Package):
The front seat heater control unit receives the requests from the rear SAM control unit via the heater LIN and then actuates the following heater pads directly:
- Left front seat cushion heater pad
- Left front seat backrest heater pad
- Front left seat adjustable seat cushion length heater pad, left (model 257, model 290 with code P65 (Seat Comfort Package))
- With code 278 (Fully electric front seats) or code 275 (Memory Package):
The driver seat control unit receives the requests from the rear SAM control unit via the interior CAN and then actuates the following heater pads directly:
- Left front seat cushion heater pad
- Left front seat backrest heater pad
- Left front seat adjustable seat cushion length heater pad, left (with code 278 (Fully electric front seats))
The driver's seat control unit or the front seat heating control unit continuously checks the function of all the components involved in the seat heating and sends the corresponding status, depending on the vehicle's equipment, over the following connection:
- Except code 278 (Fully electric front seats) and except code 275 (Memory Package):
Via the heater LIN to the rear SAM control unit
- With code 278 (Fully electric front seats) or code 275 (Memory Package):
Via the interior CAN to the rear SAM control unit
Vehicles with code 90? (Seat heater Plus for driver and front passenger)
The driver seat control unit receives the requests via the rear SAM control unit via the interior CAN, and forwards them via the driver seat LIN to the driver seat heater control unit.
The driver's seat control unit actuates the following heater pads directly:
- Left front seat cushion side bolster heater pad
- Left front seat backrest side bolster heater pad
The driver seat heater control unit actuates the following heater pads directly:
- Left front seat cushion heater pad
- Left front seat backrest heater pad
To monitor the seat heater, the driver seat control unit and the driver seat heater control unit read in the signals from the corresponding heater pad temperature sensors directly, and evaluates them.
The driver seat control unit and the driver seat heater control unit continuously check the functions of all the components involved in the seat heating. The driver seat heater control unit sends the corresponding status via the driver seat-LIN to the driver seat control unit. The driver seat control unit sends the corresponding status via the interior CAN to the rear SAM control unit.
Function feedback
In accordance with the frequency with which the left front seat heater switch is operated, the rear SAM control unit sends the status of the seat heater via the interior CAN, left front door control unit and left front door LIN to the left front seat climate control switch group, which then actuates the LEDs in the left front seat heater switch accordingly.
Front passenger seat heating
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. The rear SAM control unit evaluates this and sends the request to switch on the seat heating, depending on the equipment involved, over the following connection:
Vehicles with code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger)
- Except code 278 (Fully electric front seats) and except code 275 (Memory Package):
The front seat heater control unit receives the requests from the rear SAM control unit via the heater LIN and then actuates the following heater pads directly:
- Right front seat cushion heater pad
- Right front seat backrest heater pad
- Front right seat adjustable seat cushion length heater pad, right (model 257, model 290 with code P65 (Seat Comfort Package))
- With code 278 (Fully electric front seats) or code 275 (Memory Package):
The front passenger seat control unit receives the requests from the rear SAM control unit via the interior CAN and then actuates the following heater pads directly:
- Right front seat cushion heater pad
- Right front seat backrest heater pad
- Right front seat adjustable seat cushion length heater pad, left (with code 278 (Fully electric front seats))
The front passenger's seat control unit or the front seat heating control unit continuously checks the function of all the components involved in the seat heating and sends the corresponding status, depending on the vehicle's equipment, over the following connection:
- Except code 278 (Fully electric front seats) and except code 275 (Memory Package):
Via the heater LIN to the rear SAM control unit
- With code 278 (Fully electric front seats) or code 275 (Memory Package):
Via the interior CAN to the rear SAM control unit Vehicles with code 907 (Seat heater Plus for driver and front passenger)
The front passenger seat control unit receives the requests via the rear SAM control unit via the interior CAN, and forwards them via the front passenger seat LIN to the front passenger seat heater control unit.
The front passenger seat control unit actuates the following heater pads directly:
- Right front seat cushion side bolster heater pad
- Right front seat backrest side bolster heater pad
The front passenger seat heater control unit actuates the following heater pads directly:
- Right front seat cushion heater pad
- Right front seat backrest heater pad
To monitor the seat heater, the front passenger seat control unit and the front passenger seat heater control unit read in the signals from the corresponding heater pad temperature sensors directly, and evaluates them.
The front passenger seat control unit and the front passenger seat heater control unit continuously check the functions of all the components involved in the seat heating. The front passenger seat heater control unit sends the corresponding status via the front passenger seat-LIN to the front passenger seat control unit. The front passenger seat control unit sends the corresponding status via the interior CAN to the rear SAM control unit.
Function feedback
In accordance with the frequency with which the right front seat heater switch is operated, the rear SAM control unit sends the status of the seat heater via the interior CAN, right front door control unit and right front door LIN to the right front seat climate control switch group, which then actuates the LEDs in the right front seat heater switch accordingly.
Hot stone (with code 902 (Seat heating Plus for driver and front passenger) and code 432 (Left and right dynamic multicontour seat))
Hot stone is a comfort function, in which the seat heating in the seat backrest is switched on during the massage program.
The respective multicontour seat control unit sends the request to switch on the seat heating over the interior CAN to the rear SAM control unit.
The hot stone function can be parameterized using the diagnostic tester.
Switching off automatically
The seat heater is automatically switched off when one of the following events occurs:
- Shut-off in the event of a hardware defect
If there is no corresponding request for an active actuation the seat heating is switched off.
- Deactivation in event of excess temperature of PCBs in respective control unit
- Heating stage 3 can no longer be activated if the PCB temperature is greater than 70°C.
- Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is greater than 80°C.
- At a printed circuit board temperature of more than 90°C, the seat heater can no longer be activated.
If no circuit board temperature value is present, the interior temperature value is used instead. The climate control control unit sends the interior temperature value via the interior CAN to the rear SAM control unit.
If the PCB temperature reaches more than 90°C, a fault message is stored in the fault memory. Manual reactivation requires the printed circuit board temperature to drop to T = 2°C below the corresponding temperature threshold.
- Shutoff in the event of an error (short circuit, overload or open circuit (line break))
In the event of a short circuit, an overload or a line break, the power supply of the identified heater pad is switched off. The exact source of the fault can be diagnosed using the diagnostic tester.
- Shutoff when the engine starts
When the engine is started (cold start) the seat heater is switched off for 20 seconds. For a warm start the seat heating is switched off for 3 up to 5 s. The timer control continues to run, and the LEDs in the respective seat heater switch remain switched on. No undervoltage assessment takes place during startup.
- Switching off by means of energy management
To prevent a battery from discharging, the state of charge is continuously evaluated. Depending on the situation, the seat heater is also switched off, if necessary.
If the seat heating is switched off, the LEDs in the respective seat heating switch initially remain switched on. If the on-board electrical system reaches the specified voltage again within the following 3 minutes, the seat heating starts again automatically. If the shutoff takes longer than 3 minutes, the LEDs are also switched off. If the shutoff continues and the seat heating is requested again, the LEDs light up for 1.5 s and then go out again.
- Shutoff at voltage drop
The seat heating is switched off in the event of a voltage drop.
- Shutoff after circuit 15R OFF
For circuit 15R OFF and circuit 15C ON, the timer control runs on for another 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 electronic ignition lock control unit detects a timeout error, the seat heating is switched off.
- Shutoff at end of diagnosis
The seat heating is switched off after diagnosis has been completed.
| Electrical function schematic, seat heater, front | Model 257, 290 up to model year 2021 with code 401 (Climatised front seats) Model 257, 290 up to model year 2021 with code 873 (Left and right driver's seat heating) | PE91.30-P-2056-97XBA | |
| Model 257, 290 up to model year 2021 with code 902 (Seat heater Plus for driver and front passenger) | PE91.30-P-2056-97XBB | ||
| Overview of system components of comfort heating systems | GF91.30-P-9990FR |