Audi Q7: Windshield Defogger

Windshield Defogger

• The Windshield Defogger Control Module -J505- is activated by the Comfort System Central Control Module -J393- at the request of the Front A/C Display Control Head -E87-. This request is sent via the data bus to the Comfort System Central Control Module -J393-. The Comfort System Central Control Module -J393- relays the request to the Windshield Defogger Control Module -J505-, which then switches on the heating for the Windshield Defogger -Z2-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function and refer to → Wiring diagrams, Troubleshooting & Component locations.
• The activation of the Windshield Defogger Control Module -J505- is displayed in the "Read measured values" function of the Guided Fault Finding for the Front A/C Display Control Head -E87- and the Comfort System Central Control Module -J393-. Refer to Vehicle Diagnostic Tester.
• In the "Read measured values" function of Guided Fault Finding for the Comfort System Central Control Module -J393- (and the Front A/C Display Control Head -E87-), it is shown that there is a request and why it is not being implemented if applicable. Refer to Vehicle Diagnostic Tester.
• Check the activation of the windshield defogger. Refer to Vehicle Diagnostic Tester In the "Guided Fault Finding" function.
• Windshield defogger functionality. Refer to → Chapter "Windshield Defogger Function".
• If the resistance value calculated by the Comfort System Central Control Module -J393- (displayed as measured values) is greater than 2.4 ohms or less than 1.4 ohms, check the wire connection from the Windshield Defogger Control Module -J505- to the Windshield Defogger -Z2- for a short circuit or contact resistance. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If the resistance value calculated by the Comfort System Central Control Module -J393- is greater than approximately 3.4 ohms or less than approximately 1.4 ohms, the Comfort System Central Control Module -J393- does not activate the Windshield Defogger Control Module -J505-, or it does not switch on the heating for the Windshield Defogger -Z2-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Windshield Defogger Function

The Windshield Defogger Control Module -J505--A- is activated by the Comfort System Central Control Module -J393- at the request of the Front A/C Display Control Head -E87-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function and refer to → Wiring diagrams, Troubleshooting & Component locations.

  Note

The Windshield Defogger Control Module -J505--A- is installed under the right A-pillar trim panel. Refer to → Wiring diagrams, Troubleshooting & Component locations.

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 ºC (+ 41 ºF), "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 ºC (95 ºF). Depending on the exterior temperature, the heating period is a maximum of 6 minutes (at -40ºC (-40 ºF) ).
• When selecting "defrost" mode on the Front A/C Display Control Head -E87-, the exterior temperature is less than + 5 ºC (41 ºF) and the function was not switched off via the MMI (Multi Media Interface). 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 Windshield Defogger Control Module -J505--A- activates the heating of the Windshield Defogger -Z2- if the following basic conditions are met.

• The Front A/C Display Control Head -E87- sends an activation request to the Comfort System Central Control Module -J393- and the Comfort System Central Control Module -J393- relays this request to the Windshield Defogger Control Module -J505-.
• The voltage at the Windshield Defogger Control Module -J505- is greater than 12.7 V.
• The Windshield Defogger Control Module -J505- is not overheated.

  Note

• 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" Operating Instructions.
• The Windshield Defogger Control Module -J505- is activated by the Comfort System Central Control Module -J393- via a data wire. Should there be a condition in the Windshield Defogger Control Module -J505- which does not permit the activation 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 the information that the windshield defogger is not activated to the Front A/C Display Control Head -E87-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• The electrical resistance of the plastic film conductive coating -4- in the Windshield Defogger -Z2- 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 windshield. The Windshield Defogger Control Module -J505- converts the electrical system voltage into a variable voltage which is between 25 and 48 V, depending on electrical system voltage. If a voltage at the Windshield Defogger Control Module -J505- is greater than 13.1 V, the Windshield Defogger -Z2- is activated with a voltage greater than 41 V (up to maximum 48 V). Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The windshield defogger -A- is generally constructed as follows: -1- outer window glass, -2- plastic film, -3- electrical connections, -4- plastic film with electrically conductive coating and -5- inner window glass.
• The windshield defogger -A- is connected to the Windshield Defogger Control Module -J505- via the connector -B-. Refer to → Wiring diagrams, Troubleshooting & Component locations.
• So as not to overload the vehicle electrical system, the Windshield Defogger Control Module -J505- regulates the heating output of the windshield defogger (approximately 200 W with an electrical system voltage of 12.70 V and infinite regulation to 1000 W at 13.10 V). To prevent the electrical system voltage from dropping when the windshield defogger is switched on, the Windshield Defogger Control Module -J505- permits for an output increase of a maximum of 200 W per second.
• The Windshield Defogger Control Module -J505- checks the resistance of the Windshield Defogger -Z2- so that the Windshield Defogger -Z2- is not activated when there is a short circuit or an open circuit. If the measured resistance is less than approximately 1.4 ohms (short circuit) or greater than approximately 3.4 ohms (interruption or contact resistance), the Windshield Defogger Control Module -J505- does not switch the heater on or off. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The Windshield Defogger -Z2- is only activated in the output diagnostic test mode up to a temperature of 40ºC (104 ºF) in the vehicle interior. If the temperature is higher, "Function unknown" or "Function currently unavailable" is displayed on the Vehicle Diagnostic Tester, for example. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• The switch-on function of the Windshield Defogger Control Module -J505--A- can be checked using the Analog/Digital Multimeter -FLU83III- for example. To do so, place the current probe of the Analog/Digital Multimeter -FLU83III- over the positive wire of the Windshield Defogger Control Module -J505- to the Windshield Defogger -Z2- and select the "Measure current with current probe" function on the Analog/Digital Multimeter -FLU83III-. The display on the Analog/Digital Multimeter -FLU83III- changes from approximately 0 A to greater than 7 A. Refer to → Wiring diagrams, Troubleshooting & Component locations.

Rear Window Defogger

  Note

• If there is a condition where the rear window defogger cannot be switched on (short circuit in the connection to the Rear Window Defogger Relay -J9-, interruption in the power 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 information is sent via the data bus to the Front A/C Display Control Head -E87- that indicates that the DTC memory in the Comfort System Central Control Module -J393- must be read out. Refer to 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-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If the measured voltage on the Vehicle Electrical System Control Module -J519- at terminal "30" falls below a value stored either in the Vehicle Electrical System Control Module -J519- or the Front A/C Display Control Head -E87-, the rear window defogger is switched off completely (or the output is reduced) so that the load on the Generator -C- reduced. Refer to 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 Front A/C Display Control Head -E87- remains switched on. If the defogger is switched off for longer than approximately 100 seconds, the Front A/C Display Control Head -E87- switches off the indicator lamp.
• The "Read measured values" function of Guided Fault Finding for the Front A/C Display Control Head -E87- indicates that the rear window defogger is switched on or why there is no activation even though there is a request. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The function test for the rear window defogger activation is described in Guided Fault Finding for the Comfort System Central Control Module -J393-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The activation duration of the rear window defogger is determined by various factors (coding for the rear window version in the Front A/C Display Control Head -E87-, the measured exterior temperature, etc.). If, for example, there is an exterior temperature greater than +5 ºC (41 ºF) and a certain rear window type is installed, it can be switched off after only three minutes. If the exterior temperature is less than -20 ºC (-4 ºF) and a different rear window type is installed, the maximum activation duration can be up to 20 minutes. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The rear window defogger can also be permanently switched on (until the ignition is switched off) by pressing and holding the "rear window defogger" button on the Front A/C Display Control Head -E87-. The length of time that the button needs to be pressed can be adjusted using the "Adaptation" function in the Front A/C Display Control Head -E87-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function and refer to the Owner's Manual.
• If the exterior temperature changes while driving (it becomes greater than 0 ºC (32 ºF) ), the rear window defogger is automatically switched off after the operating time stored in the Front A/C Display Control Head -E87- has elapsed. Refer to the Owner's Manual.
• A Start/Stop System is available for certain engines for this vehicle. For vehicles with a Start/Stop System, the rear window defogger can be switched off for the time in which the Stop function is active (to protect the Battery -A-). The setting for activating the Rear Window Defogger -Z1- remains stored however in the Front A/C Display Control Head -E87-. After the engine was restarted using the Start function, the rear window defogger is switched on again. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

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