Checking heated rear window Z1 — AUDI

Checking
heated rear window
Z1
Components involved in activation of heated rear window:
The operating unit (
heater control unit
J65
on vehicles without air conditioner /
air conditioning system control unit
J301
on vehicles with manually controlled air conditioner /
Climatronic control unit
J255
on vehicles with automatically controlled air conditioner) transmits the request for activation of the heated rear window via the data bus. The
onboard supply control unit
J519
then activates the
heated rear window
Z1
via the
heated rear window relay
J9
if there is no criterion preventing the activation in
J519
Vehicle diagnostic tester
(
“Guided Fault Finding”
) and
Current flow diagrams, Electrical fault finding and Fitting locations
.
Procedure
The rear window heating is switched on via button
2
on the operating unit
J65
/
J301
item A
or
J255
item B
.
When button
2
is pressed with the ignition switched on, the
onboard supply control unit
J519
is activated by the operating unit (
J65
,
J301
or
J255
) via the data bus. As soon as
J519
switches the rear window heating on (on vehicles without high-voltage system; only with engine running), the indicator lamp in button
2
lights up (
J519
sends feedback signal via data bus). The rear window heating is switched off by pressing the button again and switching off the ignition
Owner's Manual
,
Vehicle diagnostic tester
(
“Guided Fault Finding”
) and
Current flow diagrams, Electrical fault finding and Fitting locations
.
On vehicles without a high-voltage system,
Z1
is only activated via
J9
by
J519
when the engine is running. If the engine is not running on vehicles without high-voltage system, there is no activation and no feedback from
J519
and the indicator lamp in the button either is not on or goes out again shortly after the button is pressed
Owner's Manual
and
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
On vehicles with high-voltage system, the rear window heating is activated irrespective of the engine when the vehicle's drive system is active. In electric mode with the engine stopped, it is activated just as it is on vehicles without high-voltage system with the engine running.
Z1
is switched off automatically by
J519
at ambient temperatures above 0 °C after the operating time stored in
J519
(approx. 10 minutes)
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
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 stored in
J519
(approx. 10 minutes).
If the button for rear window heating remains pressed for several seconds when the rear window heating is switched on, the rear window heating will remain switched on until the button is pressed again or the ignition is switched off
Owner's Manual
.
If e.g. the voltage measured at the
onboard supply control unit
J519
at terminal 30 drops below a value stored in
J519
or in the operating unit (
J65
,
J301
or
J255
), the rear window heating output is reduced or the rear window heating is switched off completely to relieve the load on the alternator
C
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
If the activation of
Z1
has to be shut off by
J519
due to undervoltage, the indicator lamp in the button for rear window heating in the operating unit (
J65
,
J301
or
J255
) stays on. However, if it is shut off for a lengthy period,
J519
deactivates the request for activation of the indicator lamp in the button of the operating unit, and the indicator lamp in the button goes out.
On vehicles with start/stop system, the rear window heating may be switched off 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 as soon as the engine is restarted via the start function
Vehicle diagnostic tester
(
“Guided Fault Finding”
function for
onboard supply control unit
J519
).
The
“Read measured values”
function of the Guided Fault Finding routine for the operating unit (
J65
,
J301
or
J255
) indicates that the rear window heating is switched on or why there is no activation although there is a corresponding request
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
Checking activation signal from heated rear window
Vehicle diagnostic tester
,
“Guided Fault Finding”
function for
onboard supply control unit
J519