Rear window heater, function

S67.29-4503-82

Function requirements, general

 ‘‘C. 15 ON‘‘

 No undervoltage or overvoltage

 Consumer shutoff not active

 The electronic ignition lock (EZS) control unit sends the status of circuit 15 to the signal acquisition and actuation module (SAM) control unit via interior CAN.

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 on/off function sequence

 Function sequence for automatic switch-on

 Function sequence for determining operating time

 Function sequence for traffic light stop

 Consumer shutoff function sequence

Manual on/off function sequence

The rear window heater is switched on and off via rear window heater button on the FRONT heater/air conditioning control unit switch.

The FRONT heater/air conditioning control unit switch receives the signals from the rear window heater button. The FRONT heater/air conditioning control unit switch transmits the signals via air conditioning LIN to the automatic air conditioning control unit (KLA). The automatic air conditioning (AAC [KLA]) control unit transmits the signals via the interior CAN to the signal acquisition and actuation module (SAM) control unit. This actuates the rear window heater via the rear fuse and relay module.

The rear end fuse and relay module transmits the status display of the rear window heater to the signal acquisition and actuation module (SAM) control unit to confirm the function. The signal acquisition and actuation module (SAM) control unit transmits the signals via the interior CAN to the . automatic air conditioning (AAC [KLA]) control unit. The automatic air conditioning (AAC [KLA] control unit actuates the LED in the rear window heater button via the climate control LIN and the FRONT heater/air conditioning operating unit switch.

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 operating temperature of the engine more quickly, the rear window heater is switched on to max. t = 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 ME-SFI control unit (N3/34) (with ENGINE 274) transmits a switch-on request via chassis CAN, electronic ignition lock control unit (EZS) and interior CAN to the signal acquisition and actuation module (SAM) via the interior CAN. The signal acquisition and actuation module (SAM) control unit then actuates the rear window heater via the rear fuse and relay module.

Function sequence for determining operating time

The switch-on duration of the rear window heater is stored in the signal acquisition and actuation module (SAM) control unit. The switch-on time is 2 to 26 minutes depending on the outside temperature, interior temperature and vehicle speed.

The outside temperature is recorded by the outside temperature sensor. The signal acquisition and actuation module (SAM) control unit directly reads in the sensor signal. The signal acquisition and actuation module (SAM) control unit calculates the outside temperature and transmits it via the interior CAN, electronic ignition lock control unit (EZS), chassis CAN, gateway for user interface CAN and user interface CAN to the instrument cluster (IC). The instrument cluster control unit (IC) relays the signal to the multifunction display. The outside temperature is indicated in the multifunction display. Simultaneously the instrument cluster (IC [KI]) control unit sends the signal of the outside temperature displayed via user interface CAN, gateway for user interface CAN, gateway for user interface CAN, chassis CAN, electronic ignition lock (EZS) control unit and interior CAN to the signal acquisition and actuation module (SAM) control unit.

The interior temperature is recorded via the interior air temperature sensor by the automatic air conditioning (AAC [KLA]) control unit. The interior air temperature sensor is integrated in the blower with interior air temperature sensor. The blower with interior air temperature sensor is located in the area of the ignition lock. The automatic air conditioning (AAC [KLA]) control unit transmits the interior temperature via the interior CAN to the signal acquisition and actuation module (SAM) control unit.

The Electronic Stability Program (ESP) control unit transmits the vehicle speed via the chassis CAN, the electronic ignition lock (EZS) control unit and the interior CAN to the signal acquisition and actuation module (SAM) control unit.

The duty cycle is as follows:

 The normal duty cycle is 15 min.

 At outside temperatures less than 5 °C the duty cycle increases 30 seconds per degree Celsius at low outdoor temperatures, however, for a maximum of 6 minutes only (corresponding to  –7 °C).

 At outdoor temperatures less than 0°C a speed-dependent time factor is added.

If, during the heating phase, the vehicle is driven faster than

 60 km/h 1 minute is added

 70 km/h 2 minutes are added

 80 km/h 3 minutes are added

 90 km/h 4 minutes are added

 100 km/h 5 minutes (maximum value) are added

to the operating time.

 At outside temperatures of 50 °C, the switch-on 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 active (e.g. at traffic lights, function requirements circuit 15RON), then the rear window heater is switched off and the operating time does not continue to run here. If, within 5 minutes 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 for 10 seconds after the engine is started. The traffic light stop time is parameterizable via the diagnostic system in the signal acquisition and actuation module (SAM) within a range of 0 to 10 minutes.

Consumer shutoff function sequence

To ensure on-board electrical system stability during all driving cycle phases, the signal acquisition and actuation module (SAM) control unit continuously evaluates the voltage in the on-board electrical system. In event of overload situations, the signal acquisition and actuation module (SAM) control unit switches back or off various comfort functions such as the rear window heater (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 minutes, the signal acquisition and actuation module (SAM) control unit switches the rear window heater back on. The rear window heater is then operated for the remaining operating time.

However, if the consumer shutoff lasts longer than 5 minutes, the LED of the rear window heater button is also switched off. For this purpose, the signal acquisition and actuation control unit (SAM) transits the status for consumer switch-off to the automatic air conditioning control unit (AC) via the interior CAN.

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 CODE JP1 (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.

The Electronic Stability Program (ESP) control unit transmits a signal via chassis CAN, the electronic ignition lock (EZS) control unit and the interior CAN to the signal acquisition and actuation module (SAM) control unit. The energy management then switches off the rear window heater function.