Windshield Defogger Function
The request to switch on the windshield defogger by the Front A/C Display Control Head -E87- (version -A or B-) occurs under the following conditions (for an exact description. Refer to the Owner's Manual and "Infotainment/MMI" Operating Instructions):
- After every cold start of the engine if the exterior temperature is less than +5 °C (+41 °F), "Auto" mode is set on the Front A/C Display Control Head -E87- and the function is not switched off using the MMI (Multi Media Interface). Refer to the Owner's Manual and "Infotainment/MMI" Operating Instructions. The temperature on the Front A/C Display Control Head -E87- must be set so that the A/C system is in heating mode and the Left Front Upper Body Vent Temperature Sensor -G385- and Right Front Upper Body Vent Temperature Sensor -G386- do not measure more than + 35 °C. Depending on the exterior temperature, the heating period is a maximum of 6 minutes (at -40 °C (-40 °F).
- When selecting "defrost" mode on the Front A/C Display Control Head -E87-, the exterior temperature is less than + 5 °C (+41 °F), and the function was not switched off via the MMI. Depending on the exterior temperature, the heating period is between two and six minutes. As long as the activation of the Windshield Defogger -Z2- is switched on, the activation indicator lamp flashes in the Defrost . Activation only occurs when the engine is running.
The Comfort System Central Control Module -J393- activates the heating of the Windshield Defogger -Z2- via the Left Windshield Defogger Relay -J410- and the Right Windshield Defogger -J411- if the following basic conditions are met.
- The Front A/C Display Control Head -E87- sends a request to activate to the Comfort System Central Control Module -J393-.
- The voltage on the Comfort System Central Control Module -J393- is larger than the minimum voltage. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function (for the Comfort System Central Control Module -J393-).
Depending on the vehicle version, the activation of the Windshield Defogger -Z2- may be switched off via a function in the MMI (Multi Media Interface). Refer to the Owner's Manual and "Infotainment/MMI" Owner's Manual.
The Left Windshield Defogger Relay -J410- and the Right Windshield Defogger -J411- are activated by the Comfort System Central Control Module -J393- via a data wire, If there is a condition in one of the relays (Left Windshield Defogger Relay -J410- or Right Windshield Defogger -J411-) which does not allow activating of the windshield defogger, it is sent to the Comfort System Central Control Module -J393- via this data wire. The Comfort System Central Control Module -J393- then relays this information that the Windshield Defogger -Z2- is not activated to the Front A/C Display Control Head -E87-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
For these vehicles there are different version windshield defoggers pay attention to the correct allocation to the vehicle. Refer to the Parts Information and appropriate service information .
So that the vehicle electrical system is not overloaded the Comfort System Central Control Module -J393- regulates the heating output of the windshield defogger. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function (for the Comfort System Central Control Module -J393-).
The Windshield Defogger -Z2- is only activated in the output diagnostic test mode up to a temperature of 40 °C (104 °F) in the vehicle interior. If the temperature is higher, "Function unknown" or "Function currently unavailable" is displayed on the Vehicle Diagnostic Tester, for example. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.