Heat left/right outside rearview mirrors function

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. If several requests are present simultaneously, the mirror heaters are always operated at the highest possible actuation power resulting from the corresponding actuation source. The possible actuation sources have the following priority:

1 Request via heated rear window function

2 Request via temperature-dependent control

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 mirror heater

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

With the rear window heater switched on, the rear SAM control unit (N10/8) sends the status "Rear window heater active" to the left front door control unit and the right front door control unit. 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 the heated rear window function is switched off, the mirror heaters are also switched off.

 When adjustments affecting the temperature, air distribution and air quantity are made on the automatic air conditioning control and operating unit 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).

 Detailed information on the rear window heater function is given in the separate function description "Climate control function" in the partial function "Heated rear window, function".

Additional function requirements for temperature-dependent mirror heater

 "Engine running" or "drive train operational" signal on

 The "Engine running" or "Drivetrain operational" signal is sent by the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) via drive train CAN (CAN C1), drivetrain control unit (N127), chassis FlexRay (Flex E), electronic ignition lock control unit (N73) and interior CAN (CAN B) to the left front door control unit and the right front door control unit.

Function sequence for temperature-dependent mirror heater

The mirror heaters are operated depending 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 under the outside temperature is detected.

Outside temperature:

The outside temperature is detected by the outside temperature sensor (B14). The front SAM control unit (N10/6) directly reads the signal from the outside temperature sensor, uses it to calculate the outside temperature and sends a corresponding signal to the instrument cluster via interior CAN (CAN B), electronic ignition lock control unit (A1) and user interface CAN (CAN HMI). The instrument cluster calculates the outside temperature to be displayed, taking the vehicle speed as well as the engine waste heat into consideration, and sends the corrected outside temperature value via user interface CAN, electronic ignition lock control unit and interior CAN to the front door control unit and right front door control unit..

 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 humidity and temperature sensor (B38/2b3) in the rain/light sensor with additional functions (B38/2). The front SAM control unit reads in the signal from the rain/light sensor with additional function via the rain/light sensor (LIN B16) and transmits this to the left front door control unit and right front door control nit via the interior CAN, air conditioning control unit and interior CAN.

The left front door control unit actuates the mirror heater in the left outside mirror, the right front door control unit actuates the mirror heater in the right outside mirror.

 If the value of the dew point is not plausible 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 tables include information on the actuation time of the mirror heaters.

The mirror heaters are switched off if:

 Outside temperature  dew point +5 °C (programmable via diagnosis tester)

 Outside temperature > 18 °C=