Heated Windshield, Function - GF67.10-P-0002LFA
Model 222 as of model year 2018 with code 597 (Heated windshield)
Function requirements, general
- No undervoltage or overvoltage
- Circuit 15 on or pre-entry climate control function active (model 222.173)
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. 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 heatable windshield function is activated:
- by triggering the defrost function
- by triggering the pre-entry climate control function (model 222.173)
- 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 42 V, which is transformed by the windshield heater control unit. The windshield heater control unit monitors the function of the heatable windshield and sends appropriate basic data to the climate control unit via climate control LIN 2. This may be:
- Power consumption of the heatable windshield
- Temperature of the heatable windshield
- Short circuit of the heatable windshield
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.
- Status of the pre-entry climate control function (Model 222.173)
Pre-entry climate control is controlled by the climate control unit. If pre-entry climate control is active in the heating operating mode and if the outside temperature is below 10°C, the climate control unit starts the heated 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 surface 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. The comparison of the surface temperature with the dew point temperature enables any (impending) fogging of the windshield 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 or, if the engine is switched off, the "drivetrain operational" signal. The "engine running" or "drivetrain operational" signal is sent by the CDI control unit or ME-SFI [ME] control unit via the drive train CAN, powertrain control unit, chassis 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)
If the function has been activated by starting defrosting mode or the pre-entry climate control function (model 222.173), the heatable windshield is initially operated for 30 s at 100 % power depending on the temperature of the windshield. Following this, the climate control unit controls the function depending on 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/light sensor with additional functions sends this information to the climate control unit via the rain/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.
If pre-entry climate control (model 222.173) is active, the function is started 15 min. before the programmed departure time. Five minutes or less before the programmed departure time, and during the 5 minute run-on time, the heatable windshield is operated at 100 % power.
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.
Model 213 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 heatable 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 heatable windshield is operated at more than 600 W, the climate control unit sends the "Raise the idle speed" request to the CDI control unit or the ME control unit via interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN.
The heatable windshield is automatically switched off at outside temperatures above 3°C.
| Electrical function schematic for heated windshield | PE67.10-P-2051-97SEB | ||
| Overview of system components for climate control | GF83.40-P-9994LF | ||
| Overview of system components for climate control | GF83.40-Q-9994LF |