Armrest Heater, Function - GF68.20-P-4000LF
Model 217, 222
with code 906 (Front armrest heater)
Model 222
with code 907 (Rear armrest heater)
Function requirements, general
- Heat heater coded
- 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, general
The armrests in the doors, front center console and rear center console (model 222) can be heated in three heating stages. This is controlled by the seat heater. As soon as the seat heater is activated, the armrest heater is activated as well. Actuation of the heating elements can be adapted to the user's requirements. The means the user can activate and deactivate the individual heating elements via the Audio/COMAND control unit (except code 446 (Touchpad only)) or the Touchpad (with code 446 (Touchpad only)) in the "Vehicle" menu or via the remote control (model 222 with code 864 (rear entertainment system)). The selected settings are visualized in the audio/COMAND display or on the rear display (model 222 with CODE 864 (rear entertainment system)).
The armrest heater is not equipped with its own switches, use control points for seat heater.
Depending on which control point has been actuated, different heating elements are actuated:
- Driver: Driver door armrest and front center console
- Front passenger: Passenger door armrest and front center console
- Rear left: Left rear door armrest and rear center console (model 222)
- Rear right: Right rear door armrest and rear center console (model 222)
The armrest heater function comprises the following partial functions:
- Configuring the heating elements
- Switching front armrest heater on and off
- Switching rear armrest heater on and off (model 222)
Configuring the heating elements
The heating elements can be configured via the following control elements:
- Setting via Audio/COMAND control unit (except code 446 (Touchpad only)) or Touchpad (with code 446 (Touchpad only))
- Setting via remote control (model 222 with code 864 (Rear entertainment system))
Setting via Audio/COMAND control unit (except code 446 (Touchpad only)) or Touchpad (with code 446 (Touchpad only))
Configuration of actuation of the heating elements is performed on a menu-guided basis via the Audio/COMAND control unit (except code 446 (Touchpad only)) or the Touchpad (with code 446 (Touchpad only)).
The settings can be configured individually for the driver, front passenger and rear control points (model 222).
The Audio/COMAND control unit (except code 446 (Touchpad only)) sends the operation signals to the COMAND control unit (up to model year 2018) or to the head unit (as of model year 2018) via telematics CAN. The Touchpad (with code 446 (Touchpad only)) sends the operation signals to the head unit (as of model year 2018) via telematics CAN.
The COMAND control unit (up to model year 2018) or the head unit (as of model year 2018) then activates the Audio/COMAND display via telematics CAN and generates the image signals for the menu display. The image data is transmitted to the Audio/COMAND display via the LVDS line (up to model year 2018) or the HSVL line (as of model year 2018).
Parallel to display on the audio/COMAND display, the COMAND control unit (up to model year 2018) or the head unit (as of model year 2018) transmits information about the configuration 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, by way of confirmation, a status signal to the COMAND control unit (up to model year 2018) or to the head unit (as of model year 2018) in the reverse direction. The last selected configuration is stored in the rear SAM control unit.
Setting via remote control (model 222 with code 864 (Rear entertainment system))
The rear heating elements can also be configured with the remote control.
The following heating elements can be activated or deactivated via the remote control:
- Left rear seat armrest heating element
- Right rear seat armrest heating element
- Rear center console armrest heating element
The heating elements can only be activated or deactivated together.
Operation takes place via the remote control and is shown in the rear display.
The remote control sends radio signals directly to the COMAND control unit (up to model year 2018) or to the head unit (as of model year 2018) via the headphone antenna and remote control. The COMAND control unit (up to model year 2018) or the head unit (as of model year 2018) sends the operation signals to the rear entertainment control unit via MOST and activates the rear display via telematics CAN. The image data is transmitted to this rear display by the rear entertainment control unit via the LVDS line.
Parallel to display in the rear display, the COMAND control unit (up to model year 2018) or the head unit (as of model year 2018) transmits information about the configuration 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, by way of confirmation, a status signal to the COMAND control unit (up to model year 2018) or to the head unit (as of model year 2018) in the reverse direction. The last selected configuration is stored in the rear SAM control unit.
Switching front armrest heater on and off
The front armrest heater is operated via the front seat heater switch. The first heating level is selected by pressing a front seat heater switch. The second and third heating level can be selected by pressing the switch again. When the front seat heater switch is pressed a fourth time, the rear SAM control unit switches the armrest heater off. Whichever heating level is active is shown via red LEDs in the corresponding front seat heater switch (function feedback).
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.
The rear SAM control unit evaluates the status of the front seat heater switch 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. In addition, the rear SAM control unit sends a status feedback for actuation of the LEDs in the front seat heater switch via interior CAN to the front door control unit.
In response to the request, the left front door control unit actuates the left front seat armrest heating element directly as well as the LED in the left front seat heater switch via left front door LIN.
In response to the request, the right front door control unit actuates the right front seat armrest heating element directly as well as the LED in the right front seat heater switch via right front door LIN.
In response to the request, the armrest heater control unit actuates the front center console armrest heating element and the front center console hand rest heating element directly.
The armrest heating elements are each fitted with a temperature sensor. The heat output of the armrest heating elements is controlled via the evaluation of the signals of the temperature sensors. The corresponding front door control unit reads in the signals from the front seat 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 heating element temperature sensor and relays them to the rear SAM control unit via the interior CAN.
The rear SAM control unit evaluates the signals of the temperature sensors and controls the heat output of the armrest heating elements accordingly.
Switching rear armrest heater on and off (model 222)
The rear armrest heater is operated via the rear seat heater switch. The first heating level is selected by pressing a rear seat heater switch. The second and third heating level can be selected by pressing the switch again. When the rear seat heater switch is pressed a fourth time, the rear SAM control unit switches the armrest heater off. Whichever heating level is active is shown via red LEDs in the corresponding rear seat heater switch (function feedback).
The left rear door control unit reads in the status of the left rear seat heater switch via the left rear door LIN and sends this via interior CAN to the rear SAM control unit.
The right rear door control unit reads in the status of the right rear seat heater switch via the right rear door LIN and sends this via interior CAN to the rear SAM control unit.
The front SAM control unit evaluates the status of the rear seat heater switch and transmits the request to actuate the heating elements via the interior CAN to the corresponding rear door control unit and via the heater LIN to the armrest heater control unit. In addition, the rear SAM control unit sends a status feedback for actuation of the LEDs in the rear seat heater switch via interior CAN to the rear door control unit.
In response to the request, the left rear door control unit actuates the left rear seat armrest heating element directly as well as the LED in the left rear seat heater switch via left rear door LIN.
In response to the request, the right rear door control unit actuates the right rear seat armrest heating element directly as well as the LED in the right rear seat heater switch via right rear door LIN.
In response to the request, the armrest heater control unit directly actuates the rear center console armrest heating element.
The armrest heating elements are each fitted with a temperature sensor. The heat output of the armrest heating elements is controlled via the evaluation of the signals of the temperature sensors. The corresponding rear door control unit reads in the signals from the assigned rear seat armrest heating element temperature sensor and transmits them to the rear SAM control unit via the interior CAN. The armrest heater control unit reads in the signals from the rear center console armrest heating element temperature sensor and relays them to the rear SAM control unit via the interior CAN.
The rear SAM control unit evaluates the signals of the temperature sensors and controls the heat output of the armrest heating elements accordingly.
The heat output of the armrest heater depends on the selected heating level:
- Heating level 1: 35 % heat output (one LED lights up)
- Heating level 2: 65 % heat output (two LEDs light up)
- Heating level 3: 100 % heat output (three LEDs light up)
If different heating levels are set by the driver or front passenger side or by the rear (model 222), the front center console heating element armrest, the front center console hand rest heating element and the rear center console armrest heating element (model 222) are always actuated with heating level 2.
Function note:
The armrest heater is switched off automatically (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. The armrest heater is switched off automatically.
The timer control of the three heating stages can be adjusted using a diagnostic tester.
Shutoff criteria:
If one of the following situations occurs, the armrest heater is switched off automatically:
- Switching off in event of error:
The front door control units, rear door control units (model 222) or the armrest heater control unit are fitted with a protection relay. In the event of a fault, this switches off the mass supply to the heating element. After the armrest heater is switched off by the protection relay the seat heater can only be switched back after starting a new ignition cycle.
The front door control units and rear door control units (model 222) send messages to this effect via interior CAN or the armrest heater control unit via heater LIN to the rear SAM control unit.
- Shutoff after circuit 15R OFF:
During the change from circuit 15R one to circuit 15C one, the timer control runs on for 5 minutes. If, within 5 minutes, the circuit 15R is switched on again, the armrest heater is also switched on again.
- Shutoff in the event of a hardware defect:
If actuation of a heating element is detected without a currently pending request from a seat heater switch, the power supply to the heating element is switched off.
- Deactivation with undervoltage or overvoltage:
In the event of undervoltage or overvoltage, the front door control unit or rear door control unit (model 222) or the armrest heater control unit switches off the heating element. The LEDs in the seat heater switch initially remain switched on. If the on-board electrical system voltage has been stabilized to normal voltage within 3 minutes, the armrest heater starts again automatically as well. If, however, the shutoff lasts longer than 3 min, the LEDs in the seat heater switch are also switched off. If shutoff continues and the function is requested again by pressing the seat heater switch, the LEDs light up for 1.5 s and then go out. The LEDs are connected to the seat heater function. When the seat heater is active, the LEDs come on.
In addition to the undervoltage or overvoltage protection that is integrated in the front door control unit, rear door control unit (model 222) or the armrest heater control unit, attention must also be paid to the voltage control of the energy management. The armrest heater function is connected to the seat heater function, the power consumption is calculated by the rear SAM control unit.
- Deactivation for excess temperature of printed circuit boards in armrest heater control unit:
- At a printed circuit board temperature of more than 70°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 more than 90°C, the armrest heater can no longer be activated.
- Switch off in event of voltage drop:
If one of the two supply lines to the armrest heater control unit fails, the armrest heater is switched off.
- Shutoff during engine starting procedure:
If circuit 50 is on, the power supply to the armrest heater is interrupted for 20 s. This has no influence on the timer control and the actuation of the LEDs. No undervoltage assessment takes place during startup.
- Deactivation for "Time Out":
If the request from the rear SAM control unit via the interior CAN to actuate the armrest heater via the interior CAN is missing, the armrest heater is switched off.
- Deactivation for short circuit, overload or open circuit (line break):
The front door or rear door control units (model 222) or the armrest heater control unit detect a possible short circuit, overload or a line break in the heating element. Monitoring is performed over the corresponding temperature sensors. The fault sources listed can be diagnosed individually for each heating element using a diagnostic tester.
If the seat heater has been automatically shut off, the armrest heater is also shut off and can therefore not be activated.
| Function schematic for electric armrest heater | PE68.20-P-2054-97SEA | ||
| Overview of system components of comfort heating systems | GF91.30-P-9990LF |