Heat left/right outside rearview mirrors function - GF88.79-P-2000FQ
MODEL 218
Function requirements, general
- No overvoltage or undervoltage
- On-board electrical system consumer shutoff not active
- Particular (local) front power window not active
Heating 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 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 with activated heated rear window function
- Function sequence for temperature-dependent mirror heater
Additional function sequence for mirror heater with activated heated rear window function
- Circuit 15R 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 with activated heated rear window function
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 front door control units. 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.
When adjustments affecting the temperature, air distribution and air volume are made at the automatic air conditioning control and operating unit (N22/7) with the heated rear window function switched on, the symbol for the heated rear window function and the corresponding adjustment values 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 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 (CAN E) (up to 28.2.13) or chassis CAN 1 (CAN E1) (as of 1.3.13) to the front SAM control unit with fuse and relay module (N10/1) and interior CAN to the front door control units.
Function sequence for temperature-dependent mirror heater
The mirror heaters are operated depending on the following values:
- Outside temperature
- Dewpoint temperature
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 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 sensed by the vehicle interior humidity/temperature sensor (B82). The automatic air conditioning control and operating unit reads in the sensor signal via climate control (LIN B8), calculates the dew point temperature and transmits it to the front door control units via the interior CAN.
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 table indicates the actuation time for the mirror heaters.
| Outside temperature | Duration of actuation | PWM value output |
|---|---|---|
| Vehicles up to 31.5.12 | ||
| T < 15 °C | Temperature-dependent | 100 % |
| Vehicles as of 1.6.12 up to 28.2.14 | ||
| T < 15 °C | t = 10 min (once after engine start (thawing phase)) | 100 % |
| Vehicles as of 1.3.14 | ||
| T < 15 °C | t = 10 min (once after engine start (thawing phase)) | 100 % |
| T ≤-5 °C | temperature-dependent after thawing phase | 80 % |
| T = -5 bis 5 °C | temperature-dependent after thawing phase | 50 % |
| T = 5 until 15 °C | temperature-dependent after thawing phase | 20 % |
The mirror heaters are switched off if:
- Outside temperature dew point +5 °C (programmable via diagnosis tester)
- Outside temperature > 18 °C=
| Electrical function diagram for mirror heater | PE88.79-P-2055-97XAA |
| Overview of system components for electric mirror | GF88.79-P-9996FQ |