Heated rear window, function - GF67.29-P-0003SX
MODEL 216.3, 221.0/1 up to Model Year 8
| 15.03.07 | The document has been updated to this date and will no longer be subject to revision. |
Shown on model 221.0
Function requirements
- Circuit 15 ON
- Voltage not to high or too low
- Consumer shutoff not active
Function
After actuation of the heated rear window button, the upper control panel control unit sends a message via the interior CAN to the rear SAM control unit. The rear SAM control unit switches on the heated rear window with the heated rear window relay.
After feedback from the rear SAM control unit, the indicator LED in the heated rear window button switches on. Pressing again cancels the function. Simultaneously, the indicator LED in the heated rear window button extinguishes.
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 engine load. In this case, a feedback is not accomplished by the function LED.
Duty cycle
The information whether and how long the heated rear window is switched on, is stored in the rear SAM control unit. The timer control (0 to 17 min) depends on the outside temperature, the interior temperature and the vehicle speed.
- The normal duty cycle is 6 min.
- At outside temperatures below 5°C, the duty cycle is extended by 30 s for each °C the outside temperature is lower, however, to a maximum of 6 min. (corresponding to minus 7°C).
- At outside temperatures below 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).
Activation delay
At lower outside temperatures, switch-on is delayed until the vehicle interior is heated up slightly.
However, the function LED is switched on immediately to prevent irritating the driver.
Characteristics when voltage is too high or too low
Switch off by vehicle power supply control unit
The on-board power supply voltage is monitored permanently to prevent battery discharge.
The vehicle power supply control unit switches off high current loads, such as the heated rear window, in a certain sequence until the specified minimum vehicle power supply voltage is reached again.
Shutoff by rear SAM control unit
A voltage recognition features is also present in the rear SAM control unit. The switching values lie below those of the vehicle power supply control unit.
If the voltage is less than 10.5 V for 5 s or greater than 17 V for 0.7 s, the rear SAM control unit switches off the heated rear window. The indicator LED in the heated rear widow button then flashes at a frequency of 1.5 Hz. The switch on time is not decreased.
If the period during which the voltage is too high or too low lasts for longer than 30 s, the operation is deleted completely and is then necessary to switch it on again with the heated rear window button on the upper control panel control unit.
If the voltage increases to greater than 11.5 V within 30 s or drops below 16 V, the heated rear window is switched back on.
The function LED in the heated rear window button is continuously actuated.
| Heated rear window (HRW), location of components | GF67.29-P-0003-01SX | |
| Heated rear window, block diagram | GF67.29-P-0003-03SX | |
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