Windshield Defogger
Windshield Defogger
• The Windshield Defogger Control Module (J505) - A - is installed in the luggage compartment on the left in the area of the battery.
• Remove and install the windshield defogger control module - A -.
Pay attention to the following during installation and removal:
• Prior to opening cover - B -, interrupt the voltage supply to the windshield defogger control module (for example by removing the fuse).
• When removing and installing the windshield defogger control module - A -, pay particular attention to the two wire connections - C - due to a risk of short circuit when disconnecting and in the case of disconnected wires.
• Label both wire connections - C - prior to removal to ensure they are connected correctly during installation (risk of confusion at the two bolting points).
• When tightening the securing nuts for the two wire connections - C -, be sure to apply the correct tightening torque (currently 6 Nm).
• Disconnect connector - D -.
Function:
The windshield defogger control module control module - A - is activated by the comfort system central control module (J393) following a request from the Climatronic control module (J255) , via connector - D -. Refer to and Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
The request to activate the windshield defogger of the Climatronic control module is made under the following conditions (exact description, refer to Operating instructions and Infotainment/MMI Operating instructions):
• After every cold start of the engine if the outside temperature is less than + 5°C (41 °F), Auto mode is set on the Climatronic control module, and the function is not switched off via the MMI (Multi Media Interface), refer to Operating instructions and Infotainment/MMI operating instructions. The temperature must be set on the Climatronic control module such that the A/C system is in heating mode and the temperature measured by the sensors ( left vent temperature sensor (G150) , right vent temperature sensor (G151) ) must not exceed + 35°C (95 °F). Depending on the outside temperature, heating period is a maximum of 6 minutes at -40° C (-40 °F).
• When selecting defrost mode on the Climatronic control module, the outside temperature is less than + 5°C (41 °F) and the function was not switched off via the MMI (Multi Media Interface). Depending on the exterior temperature, the heating period is between 2 and 6 minutes. As long as the activation of the windshield defogger (Z2) is switched on, the activation indicator lamp flashes in the Defrost. Actuation only takes place with engine running.
The windshield defogger control module - A - activates the heater of the windshield defogger if the following basic conditions are met.
• The Climatronic control module, transmits an activation request to the comfort system central control module, and the comfort system central control module relays this request to the windshield defogger control module.
• The voltage at the windshield defogger control module is greater than 12.7 V.
• The windshield defogger control module is not overheated.
• The activation of the windshield defogger can be switched off via a function in the MMI (Multi Media Interface), refer to Operating instructions and Infotainment/MMI operating instructions.
• The windshield defogger control module is activated by the comfort system central control module via a data line. If there is a condition in the windshield defogger control module that does not allow activation of the windshield defogger, this is communicated to the comfort system central control module via this data line. The comfort system central control module then relays this information that the windshield defogger cannot be activated, to the Climatronic control module. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The electrical resistance of the metal foil in - 1 - in the windshield defogger is approximately 1.9 Ohm. A voltage greater than the electrical system voltage is needed in order to reach the maximum possible heat output of approximately 1000 W (Watt) on the front window. The windshield defogger control module converts the vehicle electrical system voltage into a variable voltage of between 25 and 48 V, depending on vehicle electrical system voltage. If a voltage at the windshield defogger control module is greater than 13.1 V, the windshield defogger is activated with a voltage greater than 41 V (up to maximum 48 V). Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• So as not to overload the vehicle electrical system, the windshield defogger control module regulates the heating output of the windshield defogger. This is approximately 200 W at an electrical system voltage of 12.7 V and is continuously regulated to 1000 W at 13.1 V. To prevent the vehicle electrical system voltage from collapsing when the windshield defogger is switched on, the windshield defogger control module allows for an output increase of maximum 200 W per second.
• To prevent activation of the windshield defogger in the event of a short circuit or open circuit, the windshield defogger control module checks the resistance of the windshield defogger. If the measured resistance is less than approximately 1.5 ohms (short circuit) or greater than approximately 3.3 ohms (open circuit or contact resistance), the windshield defogger control module does not switch the heater on or off. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The windshield defogger 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 shown in the fault read out device display. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The activation function of the windshield defogger control module can be checked with the multimeter (V.A.G 1715) for example. Place the (V.A.G 1715) current clamp over the windshield defogger control module positive wire to the windshield defogger and select the "Measure current with current clamp" function on the (V.A.G 1715). The display on the (V.A.G 1715) changes from approximately 0 A to greater than 7 A.