Rear Window Defogger With Automatically Regulated A/C System, Checking

Climatronic Control Module -J255- activation

NOTE:

If condition is present, so that the rear window heating does not turn on, for example, if there is a short circuit in the connection to the rear window or there is a interruption in the voltage supply to the Climatronic control module, then this will be stored in the control module as a malfunction. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
If the voltage on the Vehicle Electrical System Control Module -J519- to terminal 30 falls below the valued stored, the rear window defroster will be switched off completely or the power reduced to relieve the load on the generator. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
The rear window defogger is controlled by the vehicle electrical system control module only when the engine is running. If the engine is not running, there is no message from the vehicle electrical system control module and the LED in the button in the Climatronic control module will go out for the short period.
If heated rear window must be switched off due to insufficient voltage, indicator lamp in heated rear window button on Climatronic control module remains switched on, however if switch-off is to last longer than approximately 150 seconds, Climatronic control module switches off the indicator lamp.
Measuring value block of Climatronic control module indicates that Rear Window Defogger -Z1- activation is switched on or why no activation is occurring despite a request. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
Checking actuation of rear window defogger operation is described in Guided Fault Finding for A/C system for air conditioner using Vehicle Diagnosis, Testing and Information System VAS 5051.
With outside temperatures greater than 0 °C the rear window defogger is switched off automatically by Climatronic control module after the programmed operating time (approximately 10 minutes) has elapsed.
With ambient temperatures less than 0 °C in vehicles which were built from beginning of production, rear window defogger is switched off by vehicle electrical system control module after approximately 20 minutes. At a later point in time, vehicle electrical system control modules are installed (running change in production) in which rear window defogger activation remains switched on until ignition is switched off (it can be switched off and back on again manually at any time). If the temperature becomes greater than 0 °C during a driving period, switch-off of the rear window defogger occurs after the operating time stored in the Climatronic control module has elapsed (approximately 10 minutes).
From MY 2010, this vehicle has a Start/Stop System for specific engines as optional equipment. On vehicles with the Start/Stop System, the rear window defogger is switched off whenever the Stop function is active (to protect the battery). The setting for the rear window defogger remains stored in the Climatronic control module. After the engine is started again by the Start function, rear window defogger is switched on again. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.