Heat left/right outside rearview mirrors function

Function requirements, general

 No overvoltage or undervoltage

 On-board electrical system consumer shutoff not active

 Front power window not active

Heating left and right outside mirror, general

The left mirror heater (M21/4r1) in the left outside mirror (M21/4) and the right mirror heater (M21/5r1) in the right outside mirror (M21/5) 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 (N69/3) directly actuates the mirror heater in the left outside mirror. The right front door control unit (N69/4) 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

 Circuit 15 ON

 The electronic ignition lock control unit (EZS) (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 heated rear window function active, the signal acquisition and actuation module control unit (SAM) (N10/1) transmits the status "Heated rear window active" via interior CAN to the front door control units. The left front door control unit actuates the mirror heater in the left outside mirror and the right front door control unit actuates 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 can be found in the separate function description "Climate control, function", partial function "Rear window heater, function".

Additional function requirements for temperature-dependent mirror heater

 "Engine running" signal

 The signal "Engine running" is transmitted by the CDI control unit (N3/33) (with engine 651), ME/SFI control unit (N3/34) (with engine 274) or CDI control unit (N3/36) (with engine 622) via chassis CAN (CAN E) to the electronic ignition lock control unit (EZS) (N73) and from there via the interior CAN to the 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:

 Model 447.6/7, 448.7:

The outside temperature is detected by the outside temperature sensor (B14). The signal acquisition and actuated module (SAM) directly reads in the signal from the outside temperature sensor, calculates the outside temperature and transmits it to the instrument cluster control unit (IC) (A1/1) via the interior CAN. The instrument cluster (IC) 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 the interior CAN and electronic ignition lock control unit (EZS) to the front door control units.

On vehicles with code HH4 (THERMOTRONIC automatic air conditioning) or with code HH9 (Semi-controlled automatic air conditioning, TEMPMATIC) the outside temperature is transmitted additionally by the signal acquisition and actuation control unit (SAM) via the interior CAN to the air conditioning control and operating unit (AAC-V&AAC-H) (S98).

 Model 447.8, 448.8:

The outside temperature is recorded by the outside temperature sensor. The signal acquisition and actuated module control unit (SAM) directly reads in the signal from the outside temperature sensors, calculates the outside temperature and transmits this information via the interior CAN, gateway for user interface CAN (N93/4) and user interface CAN (CAN HMI) to the instrument cluster control unit (IC). The instrument cluster (IC) (A1/1) calculates the outside temperature to be displayed, taking the vehicle speed and the engine heat into consideration, and transmits the corrected outside temperature via the user interior CAN, gateway for user interface CAN, electronic ignition lock control unit (EZS) and interior CAN to the front door control units.

On vehicles with code HH4 (THERMOTRONIC automatic air conditioning) or with code HH9 (Semi-controlled automatic air conditioning, TEMPMATIC) the outside temperature is transmitted additionally by the signal acquisition and actuation control unit (SAM) via the interior CAN to the air conditioning control and operating unit (AAC) (N154).

 If the value of the outside temperature is implausible or not available, the mirror heaters are switched off permanently.

 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 value for the dew point temperature is sensed by the humidity sensor/light sensor/rain sensor) (B38/2) (with code HH9(Semi-automatic air conditioning, controlled, TEMPMATIC) or with code JF1 (Rain sensor)) or humidity sensor/light sensor/rain sensor/sun sensor (B38/3) (with code HH4 (THERMOTRONIC automatic air conditioning)). It transmits the sensed value via roof LIN (LIN B13) to the overhead control panel control unit (OCP) (N70) and from there via the interior CAN to the climate control and operating button (AAC-V&AAC-H) (S98) (model 447.6/7, 448.7) or automatic air conditioning control unit (AAC) (N154) (model 447.8, 448.8). The climate control unit transmits dew point temperature to the front door control unit via the interior CAN.

 If the value of the dew point is not plausible or a dew point value is not available, a substitute value of T = 13 °C is used (programmable via diagnostic tester).

The mirror heaters are actuated pulse width modulated. The following tables show the actuation time of the mirror heaters for various temperature ranges at decreasing or increasing temperature.

The mirror heaters are switched off at:

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

 Outside temperature > 18 °C=