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Checking electric supplementary heater > < Checking heated seat temperature sensors

A4 Mk2

Checking seat heater elements
Checking seat heater elements
Special tools, testers and other items required
t  Vehicle diagnostic, testing and information system -VAS 5051A- (with 50 A current probe -VAS 5051/9-)
t  Adapter set -V.A.G 1594C-
t  Test box -V.A.G 1598A- and adapter cable -V.A.G 1598/12-
  Note
All fuses OK → Current flow diagrams, Electrical fault finding and Fitting locations
–  Switch off ignition.
–  Remove operating and display unit, Climatronic control unit -J255- → Chapter.
   
–  Unplug connectors -D- and -F- from operating and display unit, Climatronic control unit -J255-.
–  Connect test box adapter cable -V.A.G 1598/12- to unplugged connector -D-.
–  Connect test box -V.A.G 1598A- to adapter cable -V.A.G 1598/12-
–  Measure voltage between contact “3” at connector -F- and socket “13” (earth connection) of test box -V.A.G 1598A-.
t  Specification: approx. battery voltage
–  Measure resistance between contact “1” at connector -F- (to heater element for heated driver seat cushion -Z6-) and socket “13” (earth connection) of test box -V.A.G 1598A-.
t  Specification: Resistance approx. 1.5 (.....2.5) to 25 Ω (ohms)
–  Measure resistance between contact “2” at connector -F- (to heater element in front passenger seat) and socket “13” (earth connection) of test box -V.A.G 1598A-.
t  Specification: Resistance approx. 1.5 (.....2.5) to 25 Ω (ohms)
  Note
t  Contact resistance at the various connectors may result in resistance values of up to approx. 25 Ω being measured. As soon as a voltage of 12 V is applied, this contact resistance decreases and the seat heating function is not impaired.
t  On right-hand drive vehicles, the driver seat is connected to contact “2” and the front passenger seat to contact “1”. → Current flow diagrams, Electrical fault finding and Fitting locations
t  The resistance of the seat heater elements changes with temperature (at a seat temperature of 20 °C, the resistance is approx. 1.9  Ω).
t  As resistances of less than 10 Ω cannot be measured with sufficient accuracy using workshop equipment, it is not possible to establish a short circuit in the wiring or in the seat heater elements.
t  If the resistance value is too high, check wiring to seat heater elements for open circuit and eliminate this. If the open circuit is in the seat, repair the seat → Current flow diagrams, Electrical fault finding and Fitting locations and → General body repairs, interior; Rep. Gr.72
  A87-0391
–  Plug connectors -D- and -F- to operating and display unit, Climatronic control unit -J255- (all connectors are now plugged in at operating and display unit, Climatronic control unit -J255-).
–  Guide wire to connector -F- contact “1” (contact “2” on right-hand drive vehicles) through 50 A current probe -VAS 5051/9-.
–  On vehicle diagnostic, testing and information system -VAS 5051A-, set “Multimeter measurement: 50 A current probe” mode.
–  Set both knurled wheels for heated seats (at operating and display unit, Climatronic control unit -J255-) to position “0”.
  Note
All connectors must be plugged in at the operating and display unit, Climatronic control unit -J255-.
–  Start engine.
–  Set knurled wheel for heated driver seat to position “6”.
t  Specification: Display switches from approx. 0 A to less than 10 A
–  Set knurled wheel for heated driver seat to position “0”.
t  Specification: Display switches from less than 10 A to approx. 0 A
–  Guide wire to connector -F- contact “2” (contact “1” on right-hand drive vehicles) through 50 A current probe -VAS 5051/9-.
–  Set knurled wheel for heated front passenger seat to position “6”.
t  Specification: Display switches from approx. 0 A to less than 10 A
–  Set knurled wheel for heated front passenger seat to position “0”.
t  Specification: Display switches from less than 10 A to approx. 0 A
  Note
t  Interference on the current probe may cause a slight current to be displayed with the seat heating switched off.
t  In the event of an open circuit or a short circuit in the connection to the seat temperature sensor, the output to the heater element is not switched by the operating and display unit, Climatronic control unit -J255-.
t  In the event of a short to earth in the seat heater element or in the wiring, the operating and display unit, Climatronic control unit -J255- does not switch on the heating (immediate deactivation as soon as current is too high).
t  The design of the seat heater elements differs. Depending on heater element design there is thus a possibility of the two side bolsters being constantly heated, e.g. in the event of an open circuit in the seat cushion heater element (the temperature sensor is located in the seat cushion).
  A87-0391

Checking electric supplementary heater > < Checking heated seat temperature sensors