If requested in the DTC table to check the bus:

Check how many control modules are connected to the CAN bus using the corresponding circuit diagram.
Check the control modules multi-pin connectors for correct seating.
Connect a VAG1551/1552 or VAS5051 scan tool and press the 0 button twice for the "Automatic test sequence" function.
Before checking the bus lines, check to ensure that there is not a malfunction in any of the control modules connected to the bus.

NOTE: The term "functional malfunction" signifies a malfunction which does not directly affect the bus system but instead in some way or other disrupts the functioning of the system. This may, for instance, take the form of a malfunctioning sensor. The result is that the sensor signal can no longer be processed for bus-system data transfer. Such a functional malfunction has a direct effect on the bus system. Communication with the other control modules which need the sensor signal affected is disrupted.