Function requirements, general
No overvoltage or undervoltage
On-board electrical system consumer shutoff not active
Particular (local) front power window not active
Heat left/right outside mirror, general
The mirror heater (M21/1r1) in the left outside mirror (M21/1) and the mirror heater (M21/2r1) in the right outside mirror (M21/2) are activated in combination with the rear window heater function or depending on the outside temperature.
The left door control unit (N69/1) directly actuates the mirror heater in the left outside mirror.
The right door control unit (N69/2) directly actuates the mirror heater in the right outside mirror.
The heating left/right outside mirror function comprises the following partial functions:
Function sequence for control when heated rear window is switched on
Function sequence for temperature dependent control
Additional function requirement for control with heated rear window function switched on
Terminal 15 ON
The electronic ignition lock control unit (N73) sends the status of circuit 15 via interior CAN (CAN B) to the door control units..
Function sequence for control when heated rear window is switched on
With the heated rear window function active, the rear SAM control unit with fuse and relay module (N10/2) transmits the status "Heated rear window active" via interior CAN to the door control units. The left door control unit then directly switches on the mirror heater in the left outside mirror. The right door control unit then directly switches on the mirror heater in the right outside mirror. The mirror heaters are actuated at 100% output as long as the request is present. When heated rear window function is switched off, the mirror heaters are also switched off.
When adjustments affecting the temperature, air distribution and air volume are made on the automatic air conditioning control and operating unit (N22/7), with the rear window heater switched on, the symbol for the rear window heater and the corresponding settings appear momentarily on the Audio/COMAND display (A40/8).
Additional function requirements for temperature-dependent control
"Engine running" or "drive train operational" signal on
The CDI control unit (N3/9) (diesel engine) or ME-SFI control unit (N3/10) (gasoline engine) transmits the signal "Engine running" or "Drive train operational" via chassis CAN (CAN E) (up to 29.02.2016) or chassis CAN 1 (CAN E1) (as of 01.03.2016), front SAM control unit with fuse and relay module (N10/1) and interior CAN to the door control units.
Function sequence for temperature dependent control
The temperature-dependent control for the mirror heater depends on the following values:
Outside temperature
Dewpoint temperature
The door control units compare both values with each other and switch the mirror heaters on if a dew point temperature of T = 2 °C below the outside temperature is detected.
Outside temperature:
The outside temperature is detected by the outside temperature sensor (B14). The SAM control unit directly reads in the signal of the outside temperature sensor, calculates the outside temperature and sends it to the instrument cluster (A1) over the interior CAN. The instrument cluster calculates the outside temperature to be displayed, taking into account different variables, and transmits the corrected outside temperature value via interior CAN to the door control units.
If the outside temperature value received is implausible or not available, the mirror heaters are always switched on.
Dew point temperature:
The dew point temperature is the temperature at which water vapor would condense in the outside air. The glass in the mirrors would fog up.
The dew point temperature is sensed by the vehicle interior humidity/temperature sensor (B82). The front SAM control unit reads in the signal from the vehicle interior humidity/temperature sensor via wiper/inside rearview mirror LIN (LIN 2) and transmits it to the automatic air conditioning control and operating unit via the interior CAN. The automatic climate control and operating unit transmits the dew point temperature value to the door control unit via the interior CAN.
If the value of the dew point is implausible or a dew point value is not available, a substitute dew point value of T = 13 °C is used.
The mirror heaters are pulse width modulated (PWM), i.e. performance-controlled.
The following table includes information on the actuation time for the mirror heaters.
Outside temperature | Duration of actuation | PWM output value |
Vehicles up to 31.05.2014 | ||
T < 15 °C | t = 10 min (once after engine start (thawing phase)) | 100 % |
Vehicles as of 01.06.2014 | ||
T < 15 °C | t = 10 min (once after engine start (thawing phase)) | 100 % |
T -5 °C | after thawing phase, temperature-dependent | 80 % |
T = -5 to 5 °C | after thawing phase, temperature-dependent | 50 % |
T = 5 to 15 °C | after thawing phase, temperature-dependent | 20 % |
The mirror heaters are switched off if:
Outside temperature dew point +5 °C (programmable via diagnosis tester)
Outside temperature > 18 °C
Referenced documents
- gf8879p9996rd Overview of system components for electric mirror