Heated Windshield, Function - GF67.10-P-0002FR
Model 257, 290
up to model year 2021
with code 597 (Heated windscreen)
Function requirements, general
- No undervoltage or overvoltage
- Terminal 15 ON
The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the climate control unit.
Heated windshield
The windshield can be heated for the purpose of de-icing and preventing fogging at outside temperatures below 10°C. The climate control unit controls and monitors the heated windshield function. One of two operating modes can be specified via the variant coding in the climate control unit.
In defrost operating mode, the function is operated at 100 % power.
In AUTOMATIC operating mode, the function is operated on a power-controlled basis depending on the following variables:
- Vehicle standing time
- Outside temperature
- Temperature on inside of windshield
- Fogging tendency on inside of windshield
The heated windshield function is activated when the defrosting function is triggered or if fogging is imminent on the inside of the windshield. Depending on the coded operating mode, the climate control unit calculates the specified heat output value and sends this to the windshield heater control unit via climate control LIN 2. The windshield heater control unit responds by actuating the heated windshield. The heated windshield is operated at a voltage of 48 V, which is supplied by the 48 V on-board electrical system. The windshield heater control unit monitors the function of the heated windshield. In addition, it transmits corresponding basic data, such as power absorption capacity, temperature or short circuit of the heated windshield via the air conditioning control LIN 2 to the climate control unit.
The climate control unit evaluates the following variables for controlling the function:
- Status of defrosting function
The defrosting function is started by activation of the defrosting button on the climate control operating unit. The climate control operating unit reads in the status of the defrosting button directly and sends the status to the climate control unit via the climate control LIN. When the defrosting button is pressed and the outside temperature is below 10°C, the climate control unit starts the heated windshield function. When the defrosting button is pressed again, the climate control unit ends the function.
- Outside temperature
The outside temperature is recorded by the outside temperature sensor. The front SAM control unit directly reads in the outside temperature sensor signals, calculates the outside temperature and sends the data to the climate control unit via interior CAN. At outside temperatures below 10°C, the climate control unit starts the heatable windshield function.
- Fogging tendency (fogging index)
The fogging index describes the windshield's tendency to fog up inside. The fogging index is calculated by means of the dew point temperature.
A humidity and temperature sensor is integrated in the rain/light sensor with additional functions. This sensor measures the relative air humidity and temperature directly at the inside of the windshield. These values are used by the rain/light sensor with additional functions to calculate the dew point temperature. Comparison of the windshield surface temperature with the dew point temperature enables impending fogging of the windows to be detected. The rain/light sensor with additional functions sends corresponding information via the rain/light sensor LIN, front SAM control unit and interior CAN to the climate control unit.
- Temperature on inside of windshield
- Dewpoint temperature
If fogging is impending, the climate control unit starts the heated windshield function.
- "Engine running" or "drivetrain operational" status
Operation of the heated windshield is comparably intensive in terms of energy. To ensure onboard electrical network stability is not endangered by operation of the heated windshield, the climate control unit evaluates the stability of the engine running. When the engine is switched off, the climate control unit evaluates the "Drivetrain operational" signal. The CDI control unit or the ME-SFI [ME] control unit transmits these signals via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and interior CAN to the climate control unit.
- Coolant temperature, vehicle stand time (distinction between short or long stop)
The coolant temperature is calculated by the CDI control unit or by the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit sends the coolant temperature via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control unit.
The evaluation of the coolant temperature allows conclusions about the vehicle stand time to be made.
- Vehicle speed
The vehicle speed is calculated by the instrument cluster.
Information about the vehicle speed is transmitted by the instrument cluster via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control unit.
Defrosting mode (100 % power)
The heated windshield is initially operated for 30 s at 100 % power if:
- The function was activated by starting the defrosting function and
- The temperature on the windshield is below a specific value
The climate control unit then controls the function depending on the temperature of the windshield, the coolant temperature and the vehicle speed. After 8 min. at the latest, the climate control unit switches the function off.
The temperature on the inside of the windshield is recorded by the humidity and temperature sensor in the rain/light sensor with additional functions. The rain/light sensor with additional functions reads in the signals from the humidity and temperature sensor and calculates the temperature on the inside of the windshield. The rain and light sensor with additional functions sends this information to the climate control unit via the rain and light sensor LIN, front SAM control unit and interior CAN.
At the time the function is triggered, the climate control unit also evaluates the outside temperature. If this is below 10°C, the climate control unit starts the heatable windshield function.
Power-controlled operation
If the function has been automatically activated via the fogging index, the heatable windshield is activated on a power-controlled basis. In other words, depending on the probability or presence of windshield fogging, the heatable windshield is operated at different heading powers.
The heatable windshield is initially operated for 30 s at 100 % power. After this, the climate control unit controls the power of the heatable windshield depending on the fogging index and the vehicle speed between 35 and 100 %. At vehicle speeds above 120 km/h, the climate control unit switches the function off.
With code 357 (Map navigation) or code 531 (COMAND APS):
When driving through tunnels and when outside temperatures rise, the windshield can fog up from outside. For this reason, the climate control unit activates the heated windshield at 100 % power. As soon as the windshield's temperature is 2°C higher than the outside temperature, the climate control unit switches the function off. Driving through a tunnel is detected by the GPS information. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control unit.
If the heated windshield is operated with more than 600 W, the idle speed of the engine is increased automatically. The climate control unit transmits the request "Increase idle speed" via the interior CAN, electronic ignition lock control unit, suspension FlexRay, powertrain control unit and drive CAN to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit then increases the idle speed.
The heated windshield is switched off automatically at outside temperatures above 3°C.
| Electrical function schematic for heated windshield | PE67.10-P-2051-97XBA | ||
| Overview of system components for climate control | GF83.40-P-9994FR |