Armrest Heater, Function - GF68.20-P-4002FR

Model 257, 290 

up to model year 2021 

with code 906 (Front armrest heater) 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Circuit 15R ON

The electronic ignition lock control unit sends the status of circuit 15 over the interior CAN to the rear SAM control unit.

Armrest heater function, general 

The armrest heater is not equipped with its own switches; use control points for seat heater.

For each control point various heating elements are actuated:

• Driver: Left front door armrest and front center console armrest
• Passenger: Right front door armrest and front center console armrest

The armrest heating includes the following subfunctions:

Thanks to the armrest heater, the following armrests can be heated to three heating levels:

• Left front door armrest
• Right front door armrest
• Front center console armrest

The user can adapt the actuation of the heating elements according to his/her requirements via a menu in the head unit.

• Configuration of heating elements 
• Armrest heating activation/deactivation 
• Switching off automatically 

Configuration of heating elements 

The heating elements are configured via a menu in the head unit. Individual heating elements can be activated or deactivated. In each case, the configuration is performed separately for the driver and front passenger control points.

The heat unit transmits the configuration request for the heating elements via user interface CAN, electronic ignition lock control unit to the rear SAM control unit, which processes and stores them. The rear SAM control unit transits the status signal to the heating unit in the opposite direction to confirm.

Armrest heating activation/deactivation 

The armrest heating is activated/deactivated via the seat heating switch in the respective seat climate switch group together with the seat heating. In addition, the heating output can be regulated (initial status: armrest heating deactivated, all LEDs off):

• Press once: 3 LEDs illuminate, heating level 3 of the armrest heating is activated (100 % heating output).
• Press twice: 2 LEDs illuminate, heating level 2 of the armrest heating is activated (65 % heating output).
• Press three times: 1 LED illuminates, heating level 1 of the armrest heating is activated (35 % heating output).
• Press four times: All LEDs off, the armrest heating is switched off.

Function note 

The armrest heater is automatically switched off and time-controlled. The time is controlled by 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 armrest heater is switched off automatically.

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

The front door control unit reads in the status of the seat heater switch via the front door LIN and transmits a request to the rear SAM control unit via the interior CAN. The rear SAM control unit evaluates them and transmits the request to actuate the heating elements via the interior CAN to the corresponding front door control unit and via the heater LIN to the armrest heater control unit.

The corresponding front door control unit then actuates the front door armrest heating element. The armrest heater control unit directly actuates the front center console armrest heating elements.

The temperature of the armrest heater is monitored by the temperature sensors in the corresponding heating element. The corresponding front door control unit reads in the signals from the front door armrest heating element temperature sensor and relays them to the rear SAM control unit via the interior CAN. The armrest heater control unit reads in the signals from the front center console armrest heater element temperature sensors and transmits it to the rear SAM control unit via the heater LIN.

To provide function feedback, the rear SAM control unit transmits the status of the armrest heater via the interior CAN, front door control unit and front door LIN to the corresponding seat climate control switch group, which actuates the LEDs in the front seat heater switch accordingly.

Switching off automatically 

The armrest heater is switched off automatically if one of the following events occurs:

• Shut-off in the event of a hardware defect 

  In the event of an active actuation without a corresponding request, the rear SAM control unit switches the armrest heating off.

• Deactivation for excess temperature of printed circuit boards in armrest heater control unit 
  • At a circuit board temperature above 70°C it is no longer possible to activate heating stage 3.
  • At a circuit board temperature above 80°C it is no longer possible to activate heating stage 3 and heating stage 2.
  • At a circuit board temperature above 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.

If a circuit board temperature above 90°C is reached, an error message is stored in the fault memory. Manual switch- on requires cooling down the circuit board temperature of 2°C below the corresponding temperature threshold.

• Switching off when temperature of heating elements is too high 

  The temperature of the heating elements is continuously monitored. Where there is a threat of overheating, the power supply of this heating element is switched off.

• 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 heating element identified is shut off. The precise source of the fault can be diagnosed using the diagnostic tester.

• Shutoff when the engine starts 

  When the engine is started (cold start) the armrest heater is switched off for 20 s. In the case of a warm start, the armrest heater is switched off for 3 to 5 s. The timer control expires, also the LEDs in the corresponding seat heater switch remain switched on. No undervoltage assessment takes place during startup.

• Switching off by means of energy management 

  In order to prevent the battery from discharging, the state of charge is continuously evaluated. Depending on the situation, the armrest heater is switched off if necessary.

  If the armrest heating is deactivated, the LEDs initially remain activated in the respective seat heating switch. If the on-board electrical system reaches the specified voltage again within the next 3 minutes, the armrest heater is also automatically restarted. If the switch-off time exceeds 3 min, the LEDs are switched off as well. If the switch-off continues and the armrest heater is requested again, the LEDs illuminate for 1.5 seconds and then they go off.

• Switching off in the event of a loss of power 

  In the event of a loss of power, the armrest heater is switched off.

• Switching off after circuit 15R is OFF 

  With circuit 15R OFF and circuit 15C ON, the timer control continues for 5 min. If circuit 15R is switched on again, the armrest heater is also switched on again.

• Switching off in the event of timeout error 

  If the electronic ignition lock control unit detects a timeout error, the armrest heater is switched off.

• Shutoff at end of diagnosis 

  The armrest heater is switched off after a diagnosis has been completed.

	Electrical function schematic for armrest heater		PE68.20-P-2055-97XBA
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