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Electrical checks on air conditioner > < Convenience data bus system fault(s) only displayed by operating and display unit, Climatronic control unit J255

A4 Mk2

Fault(s) in convenience data bus system also displayed in another control unit
Fault(s) in convenience data bus system also displayed in another control unit
–  Check the signal wires and the corresponding screening betwen the various control units linked to the convenience data bus system for open circuit and wiring resistance. Wiring resistance: max. 1.5 ohms → Current flow diagrams, Electrical fault finding and Fitting locations
–  Check the signal wires and the corresponding screening betwen the various control units linked to the convenience data bus system for mutual short circuit or short to earth/positive. → Current flow diagrams, Electrical fault finding and Fitting locations → Electrical system; Rep. Gr.01
  Note
t  Pay particular attention to the possibility of loose contacts in the wires and connectors.
t  If this fault is not displayed for all connected control units, the problem may be an open circuit at a connection in the wiring.
If no fault can be found and this fault is displayed for all control units linked to the convenience data bus system, the problem is in one of the connected control units.
–  Check version, encoding and adaption entered for the control unit in dash panel insert -J285-. → Parts List, → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Electrical system; Rep. Gr.01
–  Check version and encoding of other control units linked to the convenience data bus system (e.g. on-board supply control unit -J519-, steering column electronics control unit -J527-). → Parts List, → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Electrical system; Rep. Gr.01
–  Disconnect all control units except the control unit in dash panel insert -J285- (interface with drive data bus system) and the steering column electronics control unit -J527- from the convenience data bus system → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Current flow diagrams, Electrical fault finding and Fitting locations
–  Erase fault memory of control unit in dash panel insert -J285- →  "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Electrical system; Rep. Gr.01
–  Interrogate fault memory of control unit in dash panel insert -J285- and steering column electronics control unit -J527- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Electrical system; Rep. Gr.01.
If the fault in the convenience data bus system is now no longer displayed, the problem is in one of the disconnected control units.
–  Consecutively re-connect the various control units.
–  Interrogate the fault memory after connecting each control unit.
–  Replace the control unit following installation of which the fault is displayed again.
If the fault in the convenience data bus system is still displayed, there is a problem with the control unit in dash panel insert -J285- or the steering column electronics control unit -J527-.
–  Disconnect the steering column electronics control unit -J527- and connect up a different control unit (e.g. operating and display unit, Climatronic control unit -J255-). → Current flow diagrams, Electrical fault finding and Fitting locations
–  Interrogate fault memory of control unit in dash panel insert -J285- again.
  Note
The defective control unit can be established by disconnecting the steering column electronics control unit -J527- and connecting up a different control unit.
–  Replace the defective control unit.
   

Electrical checks on air conditioner > < Convenience data bus system fault(s) only displayed by operating and display unit, Climatronic control unit J255