| Initiating self-diagnosis |
| The air conditioning control unit receives information from the electrical and electronic components (information transmitters), which are processed by the control unit in compliance with the nominal values. The output signals of the control unit control the electrical components (actuators). |
| The air conditioning control unit -J301- is located behind the heating and air conditioning control. Both components form a unit that must not be disassembled. In order to rapidly determine the cause of the fault in the event of the failure of a component or a line interruption, the control unit is fitted with a fault memory that can be read with the vehicle system tester -V.A.G 1552- or → Vehicle diagnosis, testing and information system VAS 5051. |
| If malfunctions occur in the monitored sensors or components, they are stored in the fault memory with indication of the fault type. |
| Faults that only occur temporarily (sporadically) are displayed with the suffix “/SP”. Possible causes of sporadic faults are e.g. a loose contact or a momentary line interruption. If a sporadic fault no longer occurs after 50 engine starts, it is erased from the fault memory. |
| The displayed fault information refers to a “fault table” including indications on the possible causes as well as targeted repairs. |
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| The following description relates to the vehicle system tester -V.A.G 1552- using the current program card. |
| Test preconditions for self-diagnosis |
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| All fuses must be OK in compliance with the current flow diagram. |
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| Battery voltage at least 11 volts |
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| Check whether negative terminal of battery is properly connected. |
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