Rear Window Heater, Function - GF67.29-D-3002TSA

Model 907 

with code H22 (Back pane heatable) 

Block diagram 

Function requirements, general 

• Circuit 15 ON:

The electronic ignition lock (EZS) control unit transmits the circuit status of circuit 15 via the interior CAN to the SAM control unit.

• No undervoltage or overvoltage
• Consumer shutoff not active

Rear window heater, general 

If the rear window heater is active, the mirror heater 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 traffic light stop
• The normal duty cycle is t = 15 min.
• At outside temperatures of T < 5 °C, the duty cycle is extended by t = 30 s per 1 °C drop in outside temperature up to a maximum of t = 6 min (this corresponds to T = -7 °C).
• At outside temperatures of T < 0 °C, a speed-dependent time factor is also taken into consideration.

Additional duty cycle depending vehicle speed:

• v > 60 km/h, t = 1 min
• v > 70 km/h, t = 2 min
• v > 80 km/h, t = 3 min
• v > 100 km/h, t = 5 min (maximum value)

At outside temperatures of T > 50 °C, the duty cycle of the rear window heater is limited to t = 2 min to protect the rear window.

• Consumer shutoff function sequence

If adjustments affecting the temperature, air distribution, or air volume are made on the control and operating unit for the automatic climate control with the rear window heater switched on, the symbol for the rear window heater and the corresponding set values are displayed for a short time in the Audio/COMAND display control unit (A40/8).

Manual on/off function sequence 

The control and operating unit for the automatic climate control transmits the status via the climate control LIN (LIN B8) to the SAM control unit after actuation of the rear window heater button. This switches on the rear window heater via the rear window heater relay (K13/1). To confirm the function, the SAM control unit switches on the LED in the rear window heater button. To do this, the SAM control unit transmits the status of the rear window heater via the climate control LIN (LIN B8) to the control and operating unit of the automatic climate control.

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 

To reach the engine operating conditions quickly, the CDI control unit or ME-SFI control unit can request switch-in of load-intensive electrical consumers (e.g. rear window heater). The signal for switching on additional electrical consumers is transmitted by the CDI control unit or the ME-SFI control unit via suspension FlexRay to the SAM control unit.

The SAM control unit then switches on the rear window heater to increase the engine load for max t = 15 min. In this case the LED in the rear window heater button does not confirm by flashing.

Operating time: 

The information on whether and for how long the rear window heater is switched on is stored in the SAM control unit. The timer control (t = 0 to 30 min) is dependent on the outside temperature, vehicle interior temperature, and the vehicle speed. The outside temperature is registered by the outside temperature sensor; the vehicle interior temperature is registered by the interior temperature sensor (B10/4). The vehicle speed is transmitted by the instrument cluster via the interior CAN to the SAM control unit.

The duty cycle is as follows-

Function sequence for traffic light stop 

If the engine is switched off when the rear window heater is activated (e.g. traffic light stop, function requirements circuit 15R ON), the load signal for the rear window heater is switched off. The switch on time is not decreased. If circuit 15 is not switched back on within t = 5 min, the rear window heater is reactivated.

After expiration of the traffic light stop time, without circuit 15 switching on, 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 seconds after the engine start. The traffic light stop can be parameterized via the diagnostic tester in the SAM control unit in the range of t = 0 to 10 min.

Consumer shutoff function sequence 

To prevent battery discharge in all driving cycle phases, the state of charge is continuously evaluated by the SAM control unit.

Heavy power consumers such as the rear window heater are switched off as required in a defined order until the specified minimum on-board electrical system voltage is reached again.

If the SAM control unit registers for t = 1 s an undervoltage of U ≤ 10.0 V or for t = 1 s an overvoltage of U ≥ 18 V, it switches the rear window heater off. The duty cycle does not continue to elapse during the shutoff period.

If the SAM control unit switches the rear window heater off, the LED of the rear window heater button remains on for the time being.

If the state of charge normalizes again within the subsequent period of t = 5 min, the rear window heater function also starts automatically.

However, if the consumer shutoff lasts longer than t = 5 min, the LED of the rear window heater button is also switched off.

If the shutoff continues to persist and the function is requested again via the rear window heater button, the LED lights up for t = 1.5 s and then goes out.

The rear window heater function can only be requested, when the on-board electrical system management has canceled the switch-off.

Function schematic for electrical rear window heater	Model 907	PE67.29-D-2051-97TSA
Overview of system components of rear window heater		GF67.29-D-9995TSA