Heat Left/Right Outside Rearview Mirrors Function - GF88.79-P-2000FR
Model 257, 290 up to model year 2021
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) can be activated as follows:
- Priority 1: via heated rear window function
- Priority 2: via temperature-dependent control
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 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:
- Mirror heater with heated rear window function switched on
- 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.
Mirror heater with heated rear window function switched on
With the heated rear window function active, the rear SAM control unit (N10/8) 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 as long as the request is present at a capacity of 100 %. When heated rear window function is switched off, the mirror heaters are also switched off.
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) over the drive train CAN (CAN C1), powertrain control unit (N127), chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front door control units.
Temperature-dependent mirror heater
The mirror heaters are operated depending 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 2°C is below the outside temperature.
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 and the engine heat into consideration, and transmits the corrected outside temperature via the user interior CAN, electronic ignition lock control unit and interior CAN to the front door control units.
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 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 sends the dew point temperature via rain/light sensor LIN (LIN B16), front SAM control unit and interior CAN to the climate control unit (N22/1). The climate control unit transmits dew point temperature to the front door control unit via the 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.
The value of the dew point is implausible or not available, a substitute value of 13°C (programmable via diagnostic tester) is used.
The mirror heaters are pulse width modulated (PWM), i.e. performance-controlled.
| Restart or temperature range change at decreasing temperature | Thawing phase | Holding phase | ||
|---|---|---|---|---|
| Temperature range | Duration | PWM value | Duration | PWM value |
| above 5°C | 2 min | 100 % | Temperature-dependent | 30 % |
| 5 to -5°C | 5 min | 100 % | Temperature-dependent | 70 % |
| below -5°C | 10 min | 100 % | Temperature-dependent | 100 % |
| Temperature range change at increasing temperature | Thawing phase | Holding phase | ||
|---|---|---|---|---|
| Temperature range | Duration | PWM value | Duration | PWM value |
| below -2°C | 10 min | 100 % | Temperature-dependent | 100 % |
| -2 to 8°C | 5 min | 100 % | Temperature-dependent | 70 % |
| above 8°C | 2 min | 100 % | Temperature-dependent | 30 % |
The mirror heaters are switched off at:
- Outside temperature ≥ dew point +5°C (programmable via diagnosis tester)
- Outside temperature 18°C
| Electrical function diagram for mirror heater | PE88.79-P-2055-97XBA | ||
| Overview of system components for electric mirror | GF88.79-P-9996FR |