Front Heated Seats Function - GF91.30-P-0004GN

Model 166 

as of model year 2016 

with code 401 (Climatised front seats) 

Model 166 

as of model year 2016 

with code 873 (Left and right driver's seat heating) 

Model 292 

with code 401 (Climatised front seats) 

Model 292 

with code 873 (Left and right driver's seat heating) 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Circuit 15R ON

The electronic ignition lock control unit transmits the circuit 15 status via the interior CAN to the SAM control unit.

Front seat heater (SIH), general 

The seat heater enables the seat cushions and backrests of the front 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 

Operation takes place via the left front seat heater button and the right front seat heater button in the upper control panel control unit. The upper control panel control unit directly reads in the status of the left front seat heater button and right front seat heater button and sends this via battery sensor LIN to the SAM control unit. The SAM control unit evaluates the status of the respective front seat heater button and sends a corresponding request on vehicles with CODE 275 (Memory package) via interior CAN or, on vehicles except CODE 275 (Memory package) via center console switch LIN to the driver seat control unit or to the front passenger seat control unit.

The driver seat control unit then actuates the following heater pads directly:

• Left front seat sitting surface heated cushion
• Left front backrest heated cushion

The front passenger seat control unit then actuates the following heater pads directly:

• Right front seat sitting surface heated cushion
• Right front backrest heated cushion

The driver seat control unit and the front passenger seat control unit continuously check the function of all components of the seat heater involved and send the corresponding status on vehicles with CODE 275 (Memory package) via interior CAN or, on vehicles except CODE 275 (Memory package), via center console switch LIN to the SAM control unit.

In accordance with the frequency with which the respective front seat heater button is pressed, the SAM control unit sends a request to actuate the LEDs via battery sensor LIN to the upper control panel control unit. The upper control panel control unit actuates the LEDs in the respective front seat heater button accordingly.

• Press once: 3 LEDs illuminate, stage 3 of seat heater activated (P = 100%).
• Press twice: 2 LEDs illuminate, stage 2 of seat heater activated (P = 65%).
• Press three times: 1 LED lights up, stage 1 of seat heater activated (P = 35%).
• Press four times: All LEDs off, seat heater switched off.

If the front seat heater switch is pressed again with the same circuit status, heating level 3 is provided with only P = 90 % of the heat output. The heat output of the respective heating levels can be adjusted in the factory using a diagnostic tester.

Model 166

as of model year 2016

with code 401 (Climatised front seats)

Model 292

with code 401 (Climatised front seats)

When the seat ventilation is activated, heating level 1 of the seat heater is not switched off until the seat ventilation is also switched off.

Function sequence for automatic switch off 

The seat heater is automatically switched to the next lower heating level or switched off completely depending on the time. The driver seat control unit or the front passenger seat control unit is responsible for the timer control.

• Heating level 3 is active for t = 8 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 level 1 is active for t = 20 min.

  Then the seat heater is automatically switched off.

The time settings for the three heating levels can be adjusted using the diagnostic tester in the driver seat control unit or in the front passenger seat control unit.

Other shutoff criteria:

• Shutoff in the event of a hardware defect:

  If actuation of the heater pads is detected without a pending request from a front seat heater button, the power supply to the seat heater is switched off.

• Shutoff for overtemperature of PCBs in driver seat control unit or in front passenger seat control unit:

• Heating stage 3 can no longer be activated if the PCB temperature is T > 70°C.
• Heating stage 3 and heating stage 2 can no longer be activated if the PCB temperature is T > 80°C.
• The seat heater can no longer be activated if the PCB temperature is T > 90°C.

If no circuit board temperature value is present, the outside temperature value is used instead.

If the PCB temperature reaches T > 90°C, a fault message is stored in the fault memory. Manual switch on requires a cooling down of T = 2°C for the corresponding temperature threshold.

• Shutoff in the event of an error (short circuit, overload or open circuit (line break)):

  The driver seat control unit or front passenger seat control unit detects a possible short circuit, overload or line break in the respective heater pad and deactivates the voltage supply. The fault sources that have been listed can be diagnosed individually for each heater pad using a diagnostic tester.

• Shutoff during engine starting procedure:

  When the engine is started (cold start), the seat heater is deactivated for t = 20 s. During a hot start, the seat heater is deactivated for t = 3 to 5 s. The timer control continues to run, and the LEDs remain switched on. No undervoltage is detected during startup.

• Switching off by 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 switched off, the LEDs for the respective front seat heater button initially remain switched on. If the on-board electrical system reaches its on-board electrical system voltage again within the next t = 3 min, the seat heater function is automatically activated. If the shutoff lasts longer than t = 3 min, the LEDs in the respective front seat heater button are also switched off. If shutoff continues and the function is requested again by pressing the respective front seat heater button, the LEDs light up for t = 1.5 s and then go out.

• Shutoff in the event of voltage loss:

  If one of the two supply lines (circuit 30 or circuit 30g) of the driver seat control unit or front passenger seat control unit fails, the seat heater is switched off.

• Shutoff after circuit 15R OFF:

  With circuit 15R OFF and circuit 15C ON, timer control runs on for t = 5 min. If circuit 15R is switched on again, the seat heater is also switched on again.

• Shutoff in the event of "Timeout error":

  If the request of the SAM control unit for actuating the seat heater 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:

After the diagnosis has finished, the seat heater switches off.

	Electrical function schematic, seat heater, front		PE91.30-P-2056-97NBA
	Overview of system components of comfort heating systems		GF91.30-P-9990GN