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

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

General function requirements
^ Circuit 15 On
^ No undervoltage or overvoltage
^ Consumer shutoff not active

The status of circuit 15 is transmitted by the EIS control unit (N73) to the rear SAM control unit (N10/8) via the interior CAN.

Heated rear window (HHS), general
The HHS system removes ice and fog resulting from moisture on the rear window giving the driver a clear view to the rear.

When the heated rear window (R1) is switched on, the heated outside mirror is also switched on.
To quicker reach the operating conditions of the particulate filter in vehicles with diesel engine and code (474), the CDI control unit (N3/9) can switch on the heated rear window to increase the idle speed. This function is not indicated to the driver.

The HHS system comprises the following subfunctions:
^ Manual on/off function sequence
^ Function sequence for determining operating time

Manual on/off function sequence
When the rear window heater switch (N22s1) on the AAC [KLA] control and operating unit (N22) (without code (581) Comfort automatic air conditioning) or the rear window heater switch (N22/7s1) on the comfort AAC control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning is pressed the rear window heater is switched on.
The AAC [KLA] control and operating unit or the comfort AAC control and operating unit transmits the switch-on request to the rear SAM control unit (N10/8) via the interior CAN.
The rear SAM control unit actuates the rear window heater via the rear window heater relay (F4kM) in the load compartment fuse and relay box (F4).
After switching on, the rear SAM control unit transmits a corresponding signal via the interior CAN; then the AAC [KLA] control and operating unit or comfort AAC control and operating unit via the interior CAN switches on the LED in the rear window heater switch.
When the rear window heater switch is pressed again, actuation of the rear window heater is terminated and the LED in the rear window heater switch goes out.

During engine start, the rear window heater is switched off momentarily and is switched back on t = 10 s after starting.

Function sequence for determining operating time
The switch-on duration of the heated rear window is calculated by the AAC [KLA] control and operating unit or comfort AAC control and operating unit according to the outside temperature and vehicle speed. The outside temperature is determined directly by the AAC [KLA] control and operating unit or comfort AAC control and operating unit via the outside temperature indicator temperature sensor (B14). The vehicle speed is transmitted by the instrument cluster (A1) via the interior CAN.

The normal operating time is t = 15 min. This period of time is increased depending on the outside temperature and the vehicle speed.
- 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, during the heating phase, the vehicle speed is greater than
- 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) is added to the operating time.

The heated rear window switches off automatically after the corresponding time has elapsed.