Audi Workshop Service and Repair Manuals

Three or more control units communicating via a “Two-line bus system”.

Example 1: The faults stored in the fault memories indicate that the control unit -1- has no connection to control units -2- and -3-.

Control unit	Faults stored in fault memory
-1-	t  No message from control unit -2- t  No message from control unit -3-
-2-	t  No message from control unit -1-
-3-	t  No message from control unit -1-

–  Switch off ignition. –  Unplug electrical connectors on control units linked by data bus wires and check bus wires for open circuit → Current flow diagrams, Electrical fault finding and Fitting locations.

Example 2: The faults stored in the fault memories indicate that the control unit -2- does not communicate with control units -1- and -3-.

Control unit	Faults stored in fault memory
-1-	t  No message from control unit -2-
-2-	t  No message from control unit -1- t  No message from control unit -3-
-3-	t  No message from control unit -2-

–  Switch off ignition. –  Unplug electrical connectors on control units linked by data bus wires and check bus wires for open circuit → Current flow diagrams, Electrical fault finding and Fitting locations.

Example 3: The faults stored in the fault memories indicate that none of the control units can transmit or receive.

Control unit	Faults stored in fault memory
-1-	t  Control unit defective
-2-	t  Control unit defective
-3-	t  Control unit defective

–  Switch off ignition. –  Unplug electrical connectors on control units linked by data bus wires and check bus wires for short circuit → Current flow diagrams, Electrical fault finding and Fitting locations.

–  Check the bus wires for short to positive and short to earth. –  If the cause of the fault “Control unit defective” cannot be found in the data bus wires, check whether one of the control units is responsible for causing the fault. l  Electrical connectors on all control unit that communicate via the CAN data bus are unplugged. l  Ignition switched off –  Connect one of the control units. –  Connect vehicle diagnostic, testing and information system -VAS 5051 A- → Chapter. –  Switch on ignition and select the relevant vehicle system. –  Interrogate and erase the fault memory of the control unit which has been just connected. –  Terminate function “05 - Erasing fault memory” by touching ← key. –  Conclude the transfer of data with the function “06 - End output”. –  Switch the ignition off and then on again. –  Leave the ignition switched on for 10 seconds. Then interrogate the fault memory of the control unit that has just been connected. If the fault “control unit defective” is indicated: –  Renew the control unit which has just been connected. If the fault “control unit defective” is not indicated: –  Connect the next control unit and repeat the procedure.