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

Model 217 

With Code 401 (Climatised front seats) 

Model 217 

With Code 432 (Dynamic seats left and right) 

Model 217 

With Code 873 (Left and right driver's seat heating) 

Model 222 

With Code 401 (Climatised front seats) 

Model 222 

With Code 432 (Dynamic seats left and right) 

Model 222 

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 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 backrests in three stages. The user can adjust the heat to meet his requirements and gradually set the heat output distribution with the Audio/COMAND controller unit or the touchpad in the "Vehicle" menu. The selected settings are visualized on the Audio/COMAND display.

The left front seat adjustment switch group can be used to adjust the seat heater on the front passenger seat from the driver side.

Model 222 with code 275 memory package, model 217

The memory function can be used to store the current setting for the seat heater along with other settings and called up when required.

Models 222.004/057/104/157/163/173

The pre-entry climate control function facilitates an activation of the seat heater for the driver's seat for a maximum of 2 minutes after unlocking the vehicle. The driver's seat is preheated before the journey begins.

Model 217

with code 432 (Dynamic seats left and right)

with code 902 (Seat heater Plus for driver and front passenger)

Model 222

with code 432 (Dynamic seats left and right)

with code 902 (Seat heater Plus for driver and front passenger)

Depending on the interior temperature, the heater pads are energized stronger than in a normal case and therefore heat up more quickly.

The lower the interior temperature, the stronger the supply to the heater pads.

The climate control, control unit sends the interior temperature value via the interior CAN to the rear SAM control unit.

The "fast seat heater" function can be activated or deactivated via the corresponding menu in the COMAND controller unit or the head unit.

The seat heater function includes the following subfunctions:

• Seat heater (SIH) 
• Hot stone (With Code 432 (Left and right dynamic multicontour seat)) 
• Distribution of heat output of backrest/seat cushions 

Seat heater (SIH) 

The rear SAM control unit actuates the seat heater.

The seat heater is switched on and off and the heat output is regulated using the seat heater switch in the respective front seat adjustment switch group (default status seat heater deactivated, all LEDs off):

• Actuating once: 3 LEDs illuminated, stage 3 of seat heater is activated (100 % heat output).
• Actuating twice: 2 LEDs illuminated, stage 2 of seat heater is activated (65 % heat output).
• Press three times: 1 LED lights up, level 1 of seat heater is activated (35 % heat output).
• Press four times: All LEDs off, the seat heater is switched off.

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.

Depending on the status of the seat heater, the rear SAM control unit sends status feedback for actuation of the LED in the respective seat heater switch via the interior CAN to the corresponding front door control unit, which the LED actuates in the respective seat heater switch via the front door LIN.

If the seat heater is actuated again with the same terminal status, heating level 3 is only operated with 90 % heat output. The heat output of the respective heating stages can be adjusted using a diagnostic tester.

For vehicles from model year 2018, the seat heater can also be operated via the voice control system (VCS). The head unit transmits the relevant requests via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the rear SAM control unit.

Seat heater actuation, driver seat: 

The rear SAM control unit evaluates the status of the front left seat heater switch or the request via the VCS and sends corresponding requests to actuate the seat heater via the interior CAN to the driver seat control unit.

Vehicles With Code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger): 

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

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

Vehicles With Code 432 (Left and right dynamic multicontour seat): 

The driver seat control unit sends the request to actuate the heater pads over the driver seat LIN to the driver seat heater control unit.

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

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

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

• Left front seat cushion side bolster heater pad
• Left front seat backrest side bolster heater pad

Seat heater actuation, front passenger seat: 

The rear SAM control unit evaluates the status of the front right seat heater switch or the request via the VCS and sends corresponding requests to actuate the front passenger seat heater via the interior CAN to the front passenger seat control unit.

Vehicles With Code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger): 

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

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

Vehicles With Code 432 (Left and right dynamic multicontour seat): 

The front passenger seat control unit sends the request to actuate the heater pads over the front passenger seat LIN to the front passenger seat heater control unit.

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

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

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

• Right front seat cushion side bolster heater pad
• Right front seat backrest side bolster heater pad

Function notes: 

Then the seat heater is automatically switched off (timed). The timer control is realized by the rear SAM control unit.

• Heating level 3 is activated for 8 min. Then the system automatically switches to heating stage 2.
• Heating stage 2 is activated for 10 min. Then the system automatically switches to heating level 1.
• Heating level 1 is active for 20 minutes. Then the seat heater is automatically switched off.

The timer control of the three heating stages can be adjusted using a diagnostic tester.

With circuit 50 ON, the power supply of the seat heater is interrupted for t = 20 s. This has no influence on the timer control and the actuation of the LEDs. No undervoltage is detected during startup.

Hot stone (With Code 432 (Left and right dynamic multicontour seat)) 

The hot stone function is a comfort function during which the seat heater is also switched on in addition to the massage function. The seat heater is switched on as long as the massage program is active.

The massage function is started and ended using the Audio/COMAND control panel or touchpad and is shown on the Audio/COMAND display.

The respective multicontour seat control unit sends the request to switch on the seat heater via the interior CAN to the rear SAM control unit.

With the hot stone function, only the front backrest heater pads are actuated. Information on the actuation of the heater pads can be found in the Seat Heater chapter.

The hot stone function can be parameterized using the diagnostic tester.

Shutoff criteria: 

• Switching off in event of error: 

  For this purpose, the driver seat control unit and the front passenger seat control unit are equipped with an internal protection relay that shuts off the earth supply to the respective heated cushion in the event of a fault. If the seat heater was switched off by one of the protection relays, the seat heater cannot be switched on again until another ignition cycle has taken place. The driver seat control unit or the front passenger seat control unit send corresponding messages via the interior CAN to the rear SAM control unit.

• Shutoff after circuit 15R OFF: 

  When switching from circuit 15R ON to circuit 15C ON, the timer control runs on for 5 minutes. If the circuit 15R is not switched back on within 5 minutes, the seat heater is reactivated.

• Deactivation with undervoltage or overvoltage: 

  In the event of undervoltage or overvoltage, the driver seat or front passenger seat control unit switches off the seat heater. The LEDs in the respective seat heater switch initially remain activated. If the on-board electrical system has been restored to normal voltage levels within 3 minutes, the seat heater starts again automatically.

  However, if the shutoff lasts longer than 3 min, the LEDs in the respective seat heating switch are also switched off. If shutoff continues and the function is requested again by pressing the respective seat heater switch, the LEDs light up for 1.5 s and then go out.

  In addition to the undervoltage or overvoltage protection that is integrated into the driver seat control unit or the front passenger seat control unit, attention must also be paid to the voltage control of the energy management.

• Switch off in event of voltage drop: 

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

• Deactivation in the event of excess temperature of the printed circuit boards in the respective control unit: 
  • At a printed circuit board temperature of more than 7 0°C, heating level 3 can no longer be activated.
  • At a printed circuit board temperature of more than 80°C, heating level 3 and heating level 2 can no longer be activated.
  • At a printed circuit board temperature of over 90°C, the seat heater can no longer be activated.

  If no plausible printed 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.

• Shutoff in the event of a hardware defect: 

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

• Deactivation in the event of "Time Out": 

  If the request is not received via interior CAN from the rear SAM control unit to actuate the seat heater, the seat heater is switched off.

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

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

Distribution of heat output of backrest/seat cushions 

The heat output of the heater pads can be configured using the Audio/COMAND control panel or the touchpad menu.

The Audio/COMAND control panel sends the control signals via the telematics CAN to the COMAND controller unit or the head unit.

The touchpad sends the operation signals over the telematics CAN to the head unit. The COMAND controller unit or the head unit then activates the Audio/COMAND display via telematics CAN and generates the picture signals for displaying the menus. The image data is transmitted via the LVDS or HSVL line to the Audio/COMAND display.

Parallel to display on the Audio/COMAND display, the COMAND controller unit or the head unit sends the information for configuration of the heater pads via the user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit, where it is processed and saved.

The rear SAM control unit sends the "Heat output setting" status in the opposite direction to the COMAND controller unit or the head unit for confirmation. The last selected configuration is stored in the rear SAM control unit.

When saving a memory position, the current configuration is assigned to the corresponding memory location. When selecting a memory location, the respective stored configuration is activated.

Information on the actuation of the heater pads can be found in the Seat Heater chapter.

The heat output of the respective heater pads is listed in the following table, depending on the heating level.

Heating stage 1	Balance -3	Balance -2	Balance -1	Balance 0	Balance +1	Balance +2	Balance +3
Seat sitting surface heater pad	0 %	12 %	23 %	35 %	35 %	35 %	35 %
Backrest heater pad	35 %	35 %	35 %	35 %	23 %	12 %	0 %
Heating stage 2	Balance -3	Balance -2	Balance -1	Balance 0	Balance +1	Balance +2	Balance +3
Seat sitting surface heater pad	1 %	22 %	44 %	65 %	65 %	65 %	65 %
Backrest heater pad	65 %	65 %	65 %	65 %	44 %	22 %	1 %
Heating level 3	Balance -3	Balance -2	Balance -1	Balance 0	Balance +1	Balance +2	Balance +3
Seat sitting surface heater pad	1 %	34 %	67 %	100 %	100 %	100 %	100 %
Backrest heater pad	100 %	100 %	100 %	100 %	67 %	34 %	1 %

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