Rear Window Heater, Function - GF67.29-S-3002TRB
Model 447.6/7
with code W78 (Window in tailgate or hinged rear door with wipe/wash system)
Model 448.7
Shown on model 447.6/7 (with code ME0 (electric motor 85 kW))
Shown on model 447.6/7 (with engine 622, 651)
Function requirements, general
- "Circuit 15 ON"
- No undervoltage or overvoltage
- Consumer shutoff not active
The electronic ignition lock (EZS) control unit sends the status of circuit 15 to the signal acquisition and actuation module (SAM) control unit via interior CAN.
Rear window heater, general
If the rear window heater is active the heated outside mirror is always active as well.
The rear window heater function comprises the following partial functions:
- Manual on/off function sequence
- Function sequence for automatic switch-on
- Function sequence for determining operating time
- Function sequence for traffic light stop
- Consumer shutoff function sequence
Manual on/off function sequence
The rear window heater is switched on and off via the rear window heater button the climate control and operating unit (front & rear KLA).
The climate control and operating unit (front & rear KLA) receives the signals from the rear window heater button. The climate control and operating unit (front & rear KLA) transmits the signals to the signal acquisition and actuation control unit (SAM) via the interior CAN. This actuates the rear window heater via the firewall rear fuse and relay module.
The firewall fuse and relay module transmits the status display of the rear window heater to the signal acquisition and actuation module (SAM) control unit to confirm the function. The signal acquisition and actuation control unit (SAM) relays the signal to the climate control and operating unit (front & rear KLA) via the interior CAN. The climate control and operating unit (front & rear KLA) activates the LED in the rear window heater button.
The rear window heater function is terminated when the rear window heater button is pressed again. The LED goes out simultaneously.
Function sequence for automatic switch-on
Only model 447 6/7 without code ME0 (electric motor 85 kW)
To reach the operating temperature of the engine more quickly, the rear window heater is switched on to max. 15 minutes to increase the engine load In this case the LED in the rear window heater button do not confirm by flashing.
The CDI control unit or the ME-SFI control unit (N3/34) (vehicles with engine 274) transmits a switch-on request to the signal acquisition and actuation module (SAM) control unit. The signal acquisition and actuation module (SAM) control unit then actuates the rear window heater via the firewall fuse and relay module.
Function sequence for determining operating time
The switch-on duration of the rear window heater is stored in the signal acquisition and actuation module (SAM) control unit. Depending on the outside temperature, vehicle interior temperature, and the vehicle speed, it is 2 to 26 min
The outside temperature is recorded by the outside temperature sensor. The signal acquisition and actuation module (SAM) control unit directly reads in the sensor signal. The signal acquisition and actuation module (SAM) control unit calculates the outside temperature and transmits this to the instrument cluster (IC) control unit. The instrument cluster control unit (IC) relays the signal to the multifunction display. The outside temperature is indicated in the multifunction display. At the same time, the instrument cluster (IC) control unit transmits the signal of the displayed outside temperature to the signal acquisition and actuation module (SAM) control unit.
The interior temperature is sensed by climate control and operating unit (front & rear KLA) via the interior temperature sensor. The interior air temperature sensor is integrated in the blower with interior air temperature sensor. The blower with interior air temperature sensor is located in the area of the ignition lock. The climate control and operating unit (front & rear KLA) transmits the interior temperature to the signal acquisition and actuation control unit (SAM) via the interior CAN.
The vehicle speed is sent by the Electronic Stability Program (ESP) control unit to the signal acquisition and actuation module (SAM).
The duty cycle is as follows:
- The normal duty cycle is 15 min.
- At outside temperatures less than < 5°C, the duty cycle is extended by 30 s for each 1°C decrease in outside temperature, but by max. 6 min (this corresponds to -7°C).
- At outside temperatures < 0°C, a speed-dependent time factor is additionally taken into consideration.
Extended duty cycle if, during the heating phase, the following speeds are exceeded:
- 60 km/h, 1 min
- 70 km/h, 2 min
- 80 km/h, 3 min
- 90 km/h, 4 min
- 100 km/h, 5 min (maximum value)
At outside temperatures > 50°C, the duty cycle of the rear window heater is limited to 2 min to protect the rear window.
Function sequence for traffic light stop
Only model 447.6/7 without code ME0 (electric motor 85 kW)
If the engine is switched off when the rear window heater is activated (e.g. at traffic lights, function requirements "circuit 15R ON"), the rear window heater is switched off and the operating time does not continue to run here. If circuit 15 is switched back on within 5 min, the rear window heater is reactivated.
After expiration of the traffic light stop time without switching on circuit 15, the rear window heater function is switched off completely.
During engine start, the rear window heater is switched off momentarily. The rear window heater is switched back on 10 s after the engine start. The traffic light stop time can be parameterized via the diagnostic system in the signal acquisition and actuation module (SAM) control unit in the area of 0 to 10 min.
Consumer shutoff function sequence
To ensure on-board electrical system stability during all driving cycle phases, the signal acquisition and actuation module (SAM) control unit continuously evaluates the voltage in the on-board electrical system. In event of overload situations, the signal acquisition and actuation module (SAM) control unit switches back or off various comfort functions such as the rear window heater (energy management).
The operating time is not decreased. The LED in the rear window heater remains switched on.
If the on-board electrical system voltage was stabilized again within 5 min, the signal acquisition and actuation module (SAM) control unit switches the rear window heater back on. The rear window heater is then operated for the remaining operating time.
If consumer shutoff lasts longer than 5 min, the LED in the rear window heater button is also switched off. The signal acquisition and actuation control unit (SAM) transmits the status for consumer shutoff to the climate control and operating unit (front & rear KLA) via the interior CAN.
If the consumer shutoff continues and the rear window heater button is pressed again, the LED in the rear window heater button comes on for 1.5 s and then goes out.
The rear window heater can only be reactivated, when the energy management for the consumer shutoff has canceled the switch-off.
Vehicles with code JP1 (PRE-SAFE)
If the seat belts in the vehicle have to be tensioned as part of the PRE-SAFE function, the rear window heater is switched off if it was previously switched on. For this purpose, the Electronic Stability Program (ESP) control unit transmits a signal to the signal acquisition and actuation module (SAM). The energy management then switches off the rear window heater function.
| Function schematic for electrical rear window heater | Model 448.7 | PE67.29-S-2051-97VDB | |
| Model 447.6/7 with code W78 (Window in tailgate or hinged rear door with wipe/wash system) | PE67.29-S-2051-97TRB | ||
| Overview of system components for climate control | GF83.40-S-9994TRB |