GF67.29-P-0003FL Heated Rear Window, Function

GF67.29-P-0003FL Heated Rear Window, Function

Function requirements, general
^ Circuit 15 On
^ Voltage not to high or too low
^ Consumer shutoff not active

The electronic ignition lock control unit (N73) transmits circuit 15 status to the front SAM control unit with fuse and relay module (N10/1) via the interior CAN (CAN B).

Heated rear window, general
If the heated rear window is active, the heated outside mirror is always active as well.

The heated rear window system consists of the following partial functions:
^ Manual on/off function sequence
^ Function sequence for automatic switch-on (with diesel engine and code (474) Particulate filter)
^ Function sequence for operating time
^ Function sequence for traffic light stop
^ Consumer shutoff function sequence
^ Function sequence for switching off rear window heater with PRE-SAFE "activated"

Manual on/off function sequence
The automatic air conditioning control and operating unit (N22/7) transmits a switch-on request to the rear SAM control unit with fuse and relay module (N10/2) after actuating the rear window heater button (N22/7s1) via the interior CAN. The rear SAM control unit switches on the rear window heater (R1) over the rear window heater relay (N10/2kC). The rear SAM control unit switches off the LED in the rear window heater button to confirm the function.
The rear window heater function is terminated when the rear window heater button is reactuated. The LED goes out simultaneously.

Function sequence for automatic switch-on (with diesel engine and code (474) Particulate filter)
To reach the operating conditions of the particulate filter more quickly, the CDI control unit (N3/9) can switch on the heated rear window to increase the engine load for max. t = 15 min. In this case, a feedback is not accomplished by the LED.

Function sequence for operating time
The information whether and how long the heated rear window is switched on, is stored in the rear SAM control unit. The timer control (t = 0 min. to t = 30 min.) depends on the outside temperature, the interior temperature and the vehicle speed. The outside temperature is detected by the outside temperature sensor (B14). The values are read in by the front SAM control unit and transmitted tot he rear SAM control unit via the interior CAN. The interior temperature is transmitted by the automatic air conditioning control and operating unit to the rear SAM control unit via the interior CAN. The vehicle speed is transmitted by the instrument cluster (A1) to the rear SAM control unit via interior CAN.

The duty cycle is as follows:
- 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 temperature up to a maximum of t = 6 min. (corresponding to a temperature of T = -7 °C).
- At outside temperatures of T < 0 °C, a speed-dependent time factor is also taken into consideration.
If the vehicle is operated during the heating phase at a speed greater than
- 60 km/h, the duty cycle is increased by 1 min.
- at 70 km/h, by 2 min.
- at 80 km/h, by 3 min.
- at 90 km/h, by 4 min.
- at 100 km/h, by 5 min. (maximum value).

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

Function sequence for traffic light stop
15R If the engine is switched off with the rear window heater active (e.g. traffic light stop, function requirements c. ON), the load signal for the rear window heater is switched off, however, the switch-on time does not continue to run. If, within t = 5 min. c. 15 is not switched back on, the rear window heater is reactivated. After expiration of the traffic light stop time without switching on c. 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 t = 10 s after the engine is started.
The traffic stop light time can be parameterized with the diagnosis tester in the rear SAM control unit with range t = 0 min. to t = 10 min.

Consumer shutoff function sequence
In order to prevent the battery from discharging in all driving cycle phases, the state of charge is continuously evaluated by the rear SAM control unit. Heavy power consumers such as the rear window heater are switched off as required in a defined order unit the specified minimum on-board electrical system voltage is reached again.
If the rear SAM control unit detects for t = 1 s an undervoltage of U ≤ 10.0 V or for t = 1 s an overvoltage of U ≥ 18 V, the rear SAM control unit switches off the rear window heater. The duty cycle does not continue to elapse during the shutoff period.

If the rear SAM control unit switches off the rear window heater, the LED in the rear window heater button remains on for the time being. If the on-board electrical system reaches its normal voltage within the next t = 5 min., the rear window heater function is automatically reactivated.
However, if the consumer shutoff lasts longer than t = 5 min., the LED of the rear window heater button is also switched off.

If switch-off continues and the function is requested again with the rear window heater button, the LED comes on 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 sequence for switching off rear window heater with PRE-Safe "activated"
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 (N30/4) (without code (233) DISTRONIC PLUS) or the electronic stability program control unit Premium (N30/7) (with code (233) DISTRONIC PLUS) transmits a signal via the chassis CAN (CAN E) to the front SAM control unit with fuse and relay, which relays the message to the rear SAM control unit via the interior CAN. The on-board electrical system management then switches off the rear window heater.