Rear Window Defogger
If there is a condition preventing the rear window defogger to be switched on (short circuit in the connection to the Rear Window Defogger Relay -J9-, open circuit in the voltage supply to the Comfort System Central Control Module -J393-, etc.), this is stored as a malfunction in the Comfort System Central Control Module -J393- and the information is sent via the data bus/Data Bus On Board Diagnostic Interface -J533- to the control head, the Climatronic Control Module -J255- indicating that the event memory in the Comfort System Central Control Module -J393- must be read out. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. The activation of the Rear Window Defogger -Z1- is displayed in the measured value of the Comfort System Central Control Module -J393-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding".
If the voltage at terminal "30" measured at the Vehicle Electrical System Control Module -J519- falls below a value stored in the Vehicle Electrical System Control Module -J519- or the control head, the Climatronic Control Module -J255-, the rear window defogger is switched off completely (or the power is reduced), therefore reducing the load on the Generator -C-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
If the activation of the Rear Window Defogger -Z1- must be switched off due to insufficient voltage, the indicator lamp in the rear window defogger button in the Climatronic Control Module -J255- control head remains on. If it takes longer than approximately 100 seconds to switch off, the Climatronic Control Module -J255- will switch off the indicator lamp.
The Guided Fault Finding "Read measured values" function for the Climatronic Control Module -J255- control head shows that the rear window defogger is switched on or why it was not activated even though there was a request. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
The function test for the activation of the rear window defogger is described in the Guided Fault Finding for the Comfort System Central Control Module -J393- Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
The duration of the activation of the rear window defogger is determined by various factors (coding and version of the rear window in the Climatronic Control Module -J255-, the measured outside temperature, etc.). For example, at an outside temperature of greater than +5 °C (+ 41 °F) and a certain type of rear window, it can be switched off after only three minutes, while the maximum activation duration can be up to 20 minutes if the outside temperature is less than -20 °C (-4 °F) and there is another type of rear window installed. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
Activate the rear window defogger by holding down the button for the "rear window defogger button" -5- for a while on the Climatronic Control Module -J255- control head. It will also remain turned on however (until the ignition is turned off). The time for which the button needs to be pressed can be set via the "Adaptation" function in the Climatronic Control Module -J255- Vehicle Diagnostic Tester in the "Guided Fault Finding" Function and Operating Instructions.
The rear window defogger turns off automatically if the outside temperature changes (for example raises above 0 °C (32 °F)) while driving according to the procedure in the Climatronic Control Module -J255- control head. Refer to Operating Instructions.
A start-stop system is available for certain engines of this vehicle. For vehicles with a Start/Stop System, the rear window defogger is switched off while the stop function is active (to protect the Battery -A-). The setting for the activation of the Rear Window Defogger -Z1- remains stored, however, in the Climatronic Control Module -J255- control head. After the engine was started again via the start function, the rear window defogger is switched on again. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.