Rear Window Heater, Function - GF67.29-P-3002FG
Model 213
up to model year 2021
Function requirements, general
- Terminal 15 ON
- No undervoltage or overvoltage
- Consumer shutoff not active
The electronic ignition lock control unit sends the status of circuit 15 over the interior CAN to the rear SAM control unit.
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 switching on and off:
- Switching on automatically
- Determination of operation time
- Traffic light stop
- Consumer shutoff
Manual switching on and off:
The rear window heater can be switched on and off via the rear window heater button on the climate control operating unit or the voice control system (VCS) (with code 531 (COMAND APS)).
Rear window heater button
The signals from the rear window heater button are read in over the air conditioning control LIN by the climate control, control unit. The climate control, control unit sends the signals over the interior CAN to the rear SAM control unit. This switches on the rear window heater over the rear window heater relay in the rear fuse and relay module. To confirm the function, the rear SAM control unit transmits the status "Rear window heater activated" to the climate control unit via the interior CAN. The climate control unit actuates the LED in the rear window heater button via the air control LIN.
The rear window heater function is terminated when the rear window heater button is pressed again. The LED goes out simultaneously.
VCS (with code 531 (COMAND APS))
The VCS is integrated in the head unit. 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. The climate control, control unit transmits the signal to the rear SAM control unit via the interior CAN. This switches on the rear window heater over the rear window heater relay in the rear fuse and relay module.
Switching on automatically
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 does not confirm by flashing.
The CDI control unit or the ME-SFI control unit transmits the switch-on request to the rear SAM control unit via engine CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN. The rear SAM control unit directly actuates the rear window heater via the rear window heater relay.
The rear window heater function can also be automatically activated/deactivated by the pre-entry climate control function (in hybrid vehicles).
Determination of operation time
The switch-on duration of the rear window heater is stored in the rear SAM control unit. Depending on the outside temperature, the interior temperature and vehicle speed is 2 to 26 min.
The outside temperature is recorded by the outside temperature sensor. The front SAM control unit reads in the sensor signal directly, uses it to calculate the outside temperature, and sends it via the interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster. The instrument cluster sends displayed outside temperature via user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit.
The interior temperature is recorded by the interior temperature sensor with integrated fan in the overhead control panel control unit. The overhead control panel control unit transmits the interior temperature to the climate control unit via the interior CAN. The climate control, control unit sends the value over the interior CAN to the rear SAM control unit.
The vehicle speed is sent by the instrument cluster over the user interface CAN, electronic ignition lock control unit and over the interior CAN to the rear SAM control unit.
The switch-on duration of the rear window heater is as follows:
- The normal duty cycle is 15 min.
- At outside temperatures below 5°C, for each 1°C below, the duty cycle is extended by 30 s but by max. 6 min (which corresponds to -7°C).
- At outside temperatures below 0°C, a speed-dependent time factor is also taken into account.
If, during the heating phase, the vehicle is driven faster than
- At vehicle speeds above 60 km/h, 1 min is added to the duty cycle.
- At vehicle speeds above 70 km/h, 2 min are added to the duty cycle.
- Vehicle speed above 80 km/h, 3 min are added to duty cycle.
- Vehicle speed above 90 km/h, 4 min are added to duty cycle.
- At vehicle speeds above 100 km/h, 5 min (maximum value) are added to the duty cycle.
At outside temperatures above 50°C, the duty cycle of the rear window heater is limited to 2 min to protect the rear window.
Traffic light stop
If the engine is switched off when the rear window heater is actuated (function requirements for circuit 15R ON), the rear window heater is also switched off, the switch-on time does not expire. 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 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 is started. The traffic light stop time is parameterizable via the diagnostic tester in the rear SAM control unit in the range of 0 to 10 min.
Consumer shutoff
To ensure vehicle onboard electrical network stability during all driving cycle phases, the front SAM control unit continuously evaluates the voltage in the onboard electrical system. In event of overload situations, the rear SAM control unit switches various convenience functions, e.g. rear window heater), to a lower level or off (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 is stabilized within 5 min minutes, the rear 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. For this purpose the front SAM control unit sends the status of the consumer shutoff via interior CAN to the rear SAM control unit.
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 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 control unit transmits the a signal to the front SAM control unit via chassis FlexRay, electronic ignition lock control unit and interior CAN. The energy management then switches off the rear window heater function.
| Function schematic for electrical rear window heater | PE67.29-P-2051-97DBA | ||
| Overview of system components for climate control | GF83.40-P-9994FG |