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HOMESERVICE MANUALSAUDI2004A4 BASE, 4D SEDAN, 3.0 TREPAIR AND DIAGNOSIS (SINGLE PAGE)ACCESSORIES & EQUIPMENTHEATED GLASS/DEFOGGERSON BOARD DIAGNOSTIC (OBD)WINDSHIELD DEFROSTERWINDSHIELD DEFROSTER, FUNCTION
2004 Audi A4 Base, 4D Sedan, 3.0 T

Windshield defroster, function

2004 Audi A4 Base, 4D Sedan, 3.0 TSECTION Windshield defroster, function
  • The Heated Windshield Control Module -J505- is activated by the A/C control module (see READ MEASURING VALUE BLOCK (FUNCTION 08) , display group 015):
    • After each cold start of the engine if the outside temperature is smaller than +5° C and "Auto" mode has been selected on the A/C control head -E87-. The temperature of the A/C control head -E87- has to bet set so that the air conditioning is in heating mode and none of the vent temperature sensors (-G150-, -G151-, -G261- and -G262-) should measure more than +35° C. Depending on the outside temperature, the heating period is maximum 6 minutes (at -4° C).
    • When selecting "Defrost" mode on the A/C control head -E87- and if outside temperature is smaller than +5° C. Depending on the outside temperature the heating period is between 2 and 6 minutes. As long as the windshield defroster is switched on, the indicator control light in the "Defrost" button flashes. The activation occurs only with engine running.
    • Fig 1: Identifying Heated Windshield Control Module J505
    G02752044Courtesy of AUDI OF AMERICA, INC.
  • The Heated Windshield Control Module -J505- switches on the windshield defroster, if the following conditions are met.
    • The A/C Control Head -E87- controls the Heated Windshield Control Module -J505-.
    • The voltage on Heated Windshield Control Module -J505- is greater than 12.70 volts.
    • Heated Windshield Control Module -J505- is not overheated.
  • The Heated Windshield Control Module -J505- directs approx. battery voltage to the A/C control head -E87-, with this signal the -E87- recognizes, that -J505- is ready to switch on the windshield defroster. If this voltage is cut in half (to approx. 5 to 8 volt) the Heated Windshield Control Module -J505- switches the windshield defroster on.
  • The electrical resistance of the metal foil in windshield defroster -Z2- is approx. 2.3 Ohms. In order to attain a maximum heating performance of approx. 1000 W (Watts) on the front windshield, it is necessary that the voltage is greater than the vehicle electrical system. The Heated Windshield Control Module -J505- changes the vehicle electrical voltage into a variable voltage, this variable voltage is between 25 and 48 volts depending on the vehicle electrical voltage.
    • Fig 2: Identifying Heated Windshield Control Module J505
    G02752045Courtesy of AUDI OF AMERICA, INC.
  • To avoid an overload on the vehicle electrical system, the -J505- regulates the heating output of the windshield defroster, at vehicle voltage of 12.70 the output is approx. 200 W and is gradually increased to 1000 W at 13.10 volts. To avoid the vehicle electrical system from collapsing when the windshield defroster is switched on, the Heated Windshield Control Module -J505 allows for an output increase of 200 W per second.
  • To avoid the Windshield defroster -Z2- from being activated if there is a short circuit or an open circuit, the Heated Windshield Control Module -J505- checks the resistance of the windshield defroster -Z2-. If the measured resistance is smaller than approx. 1.7 ohms (short circuit) or greater than approx. 3.3 ohms (open circuit or contact resistance) the Heated Windshield Control Module -J505- does not switch on or off the heater.
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