Function requirements, general
No overvoltage or undervoltage
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) can be activated in combination with the heated rear window function or depending on the temperature.
The left front door control unit (N69/1) directly actuates the mirror heater in the left outside mirror.
The right front 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 mirror heater when rear window is switched on
Function sequence for temperature dependent control
Additional function requirement for mirror heater when rear window heater function is 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 front door control units.
Function sequence for mirror heater when rear window is switched on
When the rear window heater function is activated, the automatic air conditioning control and operating unit (N22/7) transmits the status "Rear window heater active" to the front door control unit via the interior CAN. Then the left front door control unit switches on the mirror heater in the left outside mirror. Then the right front door control unit 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.
Detailed information on the heated rear window function is given in the function description "Automatic climate control, function" in the subfunction "Rear window heater, function".
Additional function requirements for temperature-dependent control
"Engine running" or "drive train operational" signal on
The CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) sends the "Engine running" or "Drivetrain operational" signal via chassis CAN 1 (CAN E1), electronic ignition lock control unit and interior CAN to the front 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 front 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). N10The 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 several variables and transmits the corrected outside temperature value via interior CAN to the front 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 the water vapor in the outside air condenses. The glass in the mirrors would fog up.
The dew point temperature is sensed by the humidity and temperature sensor (B38/2b3) in the rain/light sensor with additional functions (B38/2). The rain/light sensor with additional functions directly reads in the signals of the humidity and temperature sensor and sends the dew point temperature via the roof LIN (LIN B13), SAM control unit and interior CAN to the front door control units.
Then the left front door control unit switches on the mirror heater in the left outside mirror. The right front door control unit then switches on the mirror heater in the right outside mirror.
If the dew point value is implausible or unavailable, a substitute 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 |
T < 15 °C | t = 10 min (once after engine start) | 100 % |
T = 5 ... 15 °C | after thawing phase, temperature-dependent | 20 % |
T = -5 ... 5 °C | after thawing phase, temperature-dependent | 50 % |
T -5 °C | after thawing phase, temperature-dependent | 80 % |
The mirror heaters are switched off if:
Outside temperature dew point + 5 °C (programmable via diagnostic tester)
Outside temperature T > 18 °C
Referenced documents
- gf8879p9996gn Overview of system components for electric mirror