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

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

Function requirements, general
^ Circuit 15 ON
^ Voltage not to high or too low
^ Consumer shutoff not active
^ Soft top closed (on model 207.4)

The status c. 15 ON is transmitted by the electronic ignition lock control unit (N73) via the interior CAN (CAN B) to the rear SAM control unit with fuse and relay module (N10/2).
The status of the soft top is transmitted by the rear control unit (N22/6) to the rear SAM control unit via the interior CAN.

Heated rear window, general
When the rear window heater (R1) is activated, the heated outside mirror is also switched on.

The rear window heater function comprises the following subfunctions:
^ Manual on/off function sequence
^ Function sequence for automatic switch-on (on diesel engine)
^ 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
after actuating the rear window heater button (N22/7s1), the automatic air conditioning control and operating unit (N22/7) transmits a switch-on request to the rear SAM control unit via the interior CAN.
The rear SAM control unit switches on the rear window heater (N10/2kC) via the rear window heater. 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
To reach the operating conditions of the particulate filter more quickly in vehicles with diesel engine, the CDI control unit (N3/9) can switch on the rear window heater for max. t = 15 mm to increase the engine load. In this case, a feedback is not accomplished by the LED. The CDI control unit transmits a request to the chassis CAN (CAN E) to the front SAM control unit with fuse and relay module (N10/1) via the chassis CAN. It relay the request via the interior CAN to the rear SAM control unit, which actuates the rear window heater.

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 operating time depends on the outside temperature and the vehicle speed.
- The normal duty cycle is t = 15 min.
The normal operating time can be set within a range of t = 0 to 30 min. with the diagnosis tester.

- at outside temperatures of T < 5 °C, operating time is extended by t = 30 s per 1 °C drop in temperature up to a maximum of t = 6 min. (corresponding to n outside temperature of T = -7 °C). The extension of the operating time is determined by the outside temperature present when the rear window heater is switched on.
- at outside temperatures of T < 0 °C, a speed-dependent time factor is also taken into consideration.
If the rear window heater is operated at a speed greater than listed below the switch-on time is increased by the value specified:
- v = 60 km/h t = 1 min
- v = 70 km/h t = 2 min
- v = 80 km/h t = 3 min
- v = 90 km/h t = 4 min
- v = 100 km/h t = 5 min (maximum value).

The outside temperature is sensed by the outside temperature sensor (B14). The values of the outside temperature sensor are read in by the front SAM control unit. The front SAM control unit transmits the values to the rear SAM control unit via the interior CAN.

The information on the current vehicle speed is transmitted by the instrument cluster (A1) to the rear SAM control via the interior CAN.

At an outside temperature 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
If the engine is switched off when the rear window heater is activated (e.g. traffic light stop, function requirement c. 15R ON), the load signal for the rear window heater is switched off. The switch on time is not decreased. 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 switch on time is not decreased. The time the load is decreased when the engine is started, can be set from t = 0 to 60 s with the diagnosis tester.
The traffic light stop can be parameterized via the diagnosis tester in the rear SAM control unit within a range of t = 0 to 10 min.

Consumer shutoff function sequence
In order to prevent the battery from discharging in all driving cycle phases, the charging state of the on-board electrical system 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 until 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. During switch-off the switch-on time does not continue to run and the LED in the rear window heater button remains on.

If the on-board electrical system reaches its normal voltage within the next t = 5 min., the rear window heater 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 by driver, 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) (not with 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 to the front SAM control unit which relays the message to rear SAM control unit via the interior CAN. The rear window heater function is then switched off by the on-board electrical system management.