Two-Line Bus System, Checking

The DTC table indicates the bus must be checked
- Using the relevant wiring diagram, determine how many control modules are connected to the CAN-bus.
- Check that the multiple connectors of the control modules are properly connected.
- Connect the VAG1551 (or VAG1552) scan tool and press the -0- button twice to select the "Automatic Test Sequence" function 00.
- Before checking the bus lines, make sure that none of the control modules connected are malfunctioning.

Note: In this context, a malfunction means a malfunction that doesn't directly affect the bus system, but that interrupts the functioning of a system. This could be a malfunctioning sensor, for example. A malfunctioning sensor would mean that the sensor signal could no longer be used for data transfer in the bus system. This type of malfunction indirectly affects the bus system. Communication to the control modules that use the relevant sensor signal is interrupted.

Is there is a malfunction?
- Repair the malfunction before proceeding.
- Make a note of the malfunctions and erase the DTC memory in all the control modules.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Refer to the DTC table in this repair information for help in fixing malfunctions.
All malfunctions have been repaired:
- If communication to the control modules is still interrupted, check the bus lines.

While checking the bus lines, differentiate between the two situations:
^ Two control modules communicating across a "two-line bus system"
^ Three or more control modules communicating across a "two-line bus system"

Two control modules are communicating across a "two-line bus system"
- Switch ignition off.





- Disconnect both control modules.
- Check the bus lines for an open circuit.
Refer to Electrical Wiring Diagrams





- Check whether there is a short circuit between the bus lines.
Refer to Electrical Wiring Diagrams





- Check the bus lines for a short circuit to B+ or Ground (GND).
If no malfunction is found in the bus lines:
- As a test, replace one of the control modules. Select a control module that will take the least amount of time, and cost the least amount of money to replace.
- If communication between the control modules across the bus is still interrupted, replace the second control module.

Three or more control modules are communicating across a "two-line bus system"
- Analyze the DTCs stored in the memories of the control modules.

Note: This analysis will help you locate the cause of the line malfunction.

Example 1:








From the DTCs stored in the control module memories, it is determined that control module 1 is not communicating with control modules 2 and 3.
- Switch ignition off.





- Disconnect the control modules connected across the bus lines and check the bus lines for an open circuit.
Refer to Electrical Wiring Diagrams
- If no malfunction is found in the bus lines, replace control module 1.

Example 2:





From the DTCs stored in the memories, it is determined that control module 2 is not communicating with control modules 1 and 3.
- Switch ignition off.





- Disconnect the control modules connected across the bus lines and check the bus lines for an open circuit.
Refer to Electrical Wiring Diagrams
- If no malfunction is found in the bus lines, replace control module 2.

Example 3:





Using the DTCs stored in the memories, it is determined that none of the control modules are sensing or receiving signals.
- Switch ignition off.





- Disconnect the control modules connected across the bus lines and check for a short circuit between the bus lines.
Refer to Electrical Wiring Diagrams





- Check the bus lines for a short circuit to B+ or Ground (GND).
- If the cause for the DTC "Hardware malfunction" cannot be determined, check whether the DTC is caused by one of the control modules.
^ All control modules that use the CAN-bus are still disconnected. The ignition is switched off.
- Connect one of the control modules.
- Connect VAG1551 (or VAG1552) scan tool or VAS5051 tester. Switch ignition on, and erase the DTC memory of the control module you just connected. End scan tool output using the "End Output" function 06.
- Switch ignition off and then on.
- Leave ignition on for 10 seconds. Then, check the DTC memory of the control module you just connected.
- If the DTC "Hardware malfunction" is displayed, replace the control module you just connected.
- If the DTC "Hardware malfunction" is not displayed, connect the next control module and repeat the procedure.