Audi Workshop Service and Repair Manuals

Three or more control units communicating via a „two-wire bus system“

Example 1: From the entries in the event memories you can see that control unit -1- has no connection to control units -2- and -3-.

Control unit	Entry in event 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. –  Detach the electrical connectors at the control units which are linked by the bus wires and check whether there is an open circuit in one of the bus wires → Current flow diagrams, Electrical fault finding and Fitting locations.

Example 2: From the entries in the event memories you can see that control unit -2- has no connection to control units -1- and -3-.

Control unit	Entry in event 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. –  Detach the electrical connectors at the control units which are linked by the bus wires and check whether there is an open circuit in one of the bus wires → Current flow diagrams, Electrical fault finding and Fitting locations.

Example 3: From the entries in the event memories, you can see that none of the control units are able to transmit or receive signals.

Control unit	Entry in event memory
-1-	t  Control unit defective
-2-	t  Control unit defective
-3-	t  Control unit defective

–  Switch off ignition. –  Detach the electrical connectors at the control units which are linked by the bus wires and check whether there is a short circuit between the bus wires → Current flow diagrams, Electrical fault finding and Fitting locations.

–  Check the bus wires for short to positive or earth. –  If the cause of the fault „control unit defective“ cannot be found in the bus wires, check whether one of the control units is causing the fault. l  The connectors at all control units which communicate via the CAN bus are detached. l  Ignition switched off. –  Connect one of the control units. –  Connect vehicle diagnostic tester → Chapter. –  Switch on ignition and select the relevant vehicle system. –  Interrogate and erase the event memory of the control unit which has just been connected. –  Exit function „Erase event memory“ by touching ← button. –  Select function „End output“. –  Switch ignition off and on again. –  Leave the ignition switched on for 10 seconds. Then interrogate the event memory of the control unit that has just been connected. If the fault „control unit defective“ is displayed: –  Renew the control unit that has just been connected. If the fault „control unit defective“ is not displayed: –  Connect the next control unit and repeat the above procedure.