Checking heated rear window Z1, vehicles with automatically controlled air conditioner — AUDI

Checking
heated rear window
Z1
, vehicles with automatically controlled air conditioner
Procedure
The heated rear window is switched on via button
2
on the operating unit (
Climatronic control unit
J255
).
Note
When button
2
is pressed with the ignition switched on, the
onboard supply control unit
J519
is activated by the operating unit (
Climatronic control unit
J255
) via the data bus. As soon as
J519
switches the rear window heating on (only with engine running), the indicator lamp in button
2
lights up (
J519
sends feedback signal via data bus). The heated rear window is switched off by pressing button
2
again and switching off the ignition
Owner's Manual
and
Current flow diagrams, Electrical fault finding and Fitting locations
.
Situations preventing the rear window heating from being switched on (short circuit in connection to rear window, open circuit in power supply to operating unit (
Climatronic control unit
J255
) or to
onboard supply control unit
J519
) are stored as faults in the corresponding control unit
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
If the voltage measured at the
onboard supply control unit
J519
at terminal
“30”
drops below a value stored in the
J519
, the rear window heating is deactivated completely (or the power is reduced). The load on the
alternator
C
is then reduced
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
The rear window heating is only actuated by the
J519
when the engine is running. With the engine stopped, there is no feedback from the
J519
and the LED in button
2
of
J255
goes out again shortly after the button is pressed.
If the activation of
Z1
has to be shut off due to undervoltage, the indicator lamp in the button for rear window heating in
J255
stays on. However, if deactivation lasts longer than approx. 150 seconds
J255
switches off the indicator lamp.
The
“Read measured values”
function of the Guided Fault Finding routine for the operating unit (
Climatronic control unit
J255
) indicates that the rear window heating is switched on or why there is no actuation although there is a corresponding request
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
The procedure for checking the actuation of the rear window heating is described in
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
Z1
is switched off automatically by
J519
at ambient temperatures above 0 °C after the operating time stored in
J519
(approx. 10 minutes).
At ambient temperatures below 0 °C,
Z1
remains switched on until the ignition is switched off (it can be switched off and on again manually at any time). If the temperature rises above 0 °C while the vehicle is being driven,
Z1
is switched off after the operating time (approx. 10 minutes) stored in
J519
.
On vehicles with a start/stop system, the rear window heating might be deactivated while the stop function is active (to protect the
battery
A
). However, the setting for activation of
Z1
remains stored. The rear window heating is switched on again after the engine has been re-started via the start function
Vehicle diagnostic tester
(
“Guided Fault Finding”
).