Rear Window Defogger, Checking

Rear Window Defogger, Checking

• If there is a condition preventing the rear window defogger from being 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 and the information is sent via the data bus Data bus on board diagnostic interface (J533) to the Climatronic control module (J255) , indicating that the event memory in the Comfort system central control module must be read out using 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. Check using Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• 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 or the Climatronic control module (J255) , the rear window defogger is switched off completely (or the power is reduced), thus reducing the load on the Generator. Check using 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 low voltage, the indicator lamp in the rear window defogger button in the Climatronic control module stays on. However, if the deactivation takes longer than 100 seconds, the Climatronic control module switches the indicator lamp off.

• The "Read measured values" function of the Guided Fault Finding of the Climatronic control module, displays the fact that the rear window defogger is switched on or why activation did not occur despite a request. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• The function test of the activation of the rear window defogger is described using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the Comfort system central control module (J393).

• 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, 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, activation can be switched off after only 3 minutes, while the maximum activation duration can be up to 20 minutes in the case of an outside temperature of less than -20° C (68° F)and another type of rear window. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• The activation of the rear window defogger can also be continuously switched on (until the ignition is switched off) by pressing and holding the "rear window defogger" button - 5 - on the Climatronic control module. The time for which the button needs to be pressed can be set via the "Adaptation" function in the Climatronic control module using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function and the Owner's manual.






• If the outside temperature changes during a driving period (for example, becomes greater than 0° C), the rear window defogger switches off automatically after expiration of operating times stored in the Climatronic control module. Refer to the Owner's manual.