Rear Window Heater, Function - GF67.29-P-3002LF
Model 217, 222
Function requirements, general
- No undervoltage or overvoltage
- Terminal 15 ON
The electronic ignition lock control unit sends the circuit status of circuit 15 via the interior CAN to the rear SAM control unit.
Rear window heater, general
If the rear window heater is active, the mirror heater is always active too.
The rear window heater function comprises the following partial functions:
- Manually switch rear window heater on/off
- Automatically switch on rear window heater
- Establish duty cycle
- Traffic light stop
- Consumer shutoff
Manually switch rear window heater on/off
The rear window heater is switched on and off with the rear window heater button in the automatic air conditioning control and operating unit.
The climate control unit reads in the status of the rear window heater button via the climate control LIN and transmits it via the interior CAN to the rear SAM control unit. The rear SAM control unit switches on the rear window heater via 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.
Automatically switch on rear window heater
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 can also be switched on or off using the pre-entry climate control function (in model 222.004/057/104/157/163/173).
Establish duty cycle
The switch-on duration of the rear window heater is stored in the rear SAM control unit. The inside temperature and vehicle speed is max. 26 min. depending on the 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 SAM control unit via interior CAN.
The interior temperature is recorded by the interior temperature sensor in the overhead control panel control unit. The overhead control panel control unit reads in the signals of the interior temperature sensor directly, calculates the interior temperature and sends this (in vehicles up to model year 2018) via roof LIN, front SAM control unit and interior CAN to the climate control unit. In vehicles from model year 2018 and later, the overhead control panel control unit transmits the interior temperature to the climate control unit via the interior CAN. The climate control unit sends the interior temperature via the interior CAN to the rear SAM control unit.
The instrument cluster transmits the vehicle speed via user interface CAN, electronic ignition lock control unit and interior CAN to the rear SAM control unit.
The duty cycle 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 added.
If, during the heating phase, the vehicle is driven faster than:
- 60 km/h, 1 min is added to the duty cycle
- 70 km/h, 2 min are added to the duty cycle
- 80 km/h, 3 min are added to the duty cycle
- 90 km/h, 4 min are added to the duty cycle
- 100 km/h, 5 min (maximum value) are added to the duty cycle
At outside temperatures above 50°C, the rear window heater is operated for max. 2 min to protect the rear window.
Traffic light stop
If the engine is switched off while the rear window heater is activated (e.g. traffic light stop, function requirements for circuit 15R ON), the rear SAM control unit switches off the rear window heater. The operating time is not decreased.
If circuit 15 is switched back on within 5 min., 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 circuit 15 is not switched back on within 5 min., the rear SAM control unit switches the rear window heater off completely. The previously calculated operating time is deleted.
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 on-board 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.
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 "PRE-SAFE® status" to the SAM control unit via chassis FlexRay, the electronic ignition lock control unit and interior CAN. Energy management then starts consumer shutoff.
| Function schematic for electrical rear window heater | PE67.29-P-2051-97SEA | ||
| Overview of system components for climate control | GF83.40-P-9994LF |