Data exchange between control modules, checking

NOTE:

Data exchange between individual control modules occurs via a bus system.
The term "CAN-bus" refers to a system that transports and distributes data.
The wire connections between the control modules, via which data is transferred, are referred to as data wires.
Data is transferred to the connected control modules serially (one after the other) via these data wires.

Bus system, checking

The DTC table indicated that data exchange via the bus should be checked:

Check to be sure the multi-pin connectors of the control modules are securely connected.

Requirements

VAS 5051/5052 tester connected and vehicle On Board Diagnostic (OBD) selected. Refer to VAG 1551/1552 Scan Tool (ST), VAS 5051 Vehicle Diagnostic Testing and Information System or VAS 5052 Vehicle Diagnostic and Service System, connecting and selecting functions .
Ignition switched on.

Procedure

Fig 1: Diagnostic System VAS 5051: Display

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Display on VAS 5051/5052:

In selection -1-, press "00 - Check DTC Memory - complete system".

NOTE: The address word 00 initiates the automatic test sequence, i.e. it results in a DTC check on all OBD capable systems in the vehicle via rapid data transfer.

Wait until the next indication appears on display.

When a control module responds with its identification, the display indicates the number of stored errors or indicates "no malfunctions recognized".

If necessary, print out Screen content or On Board Diagnostic (OBD) protocol:

Refer to Operating instructions for VAS 5051/5052 tester

If a malfunction involving "... databus" or "... no communication" is indicated:

Check whether the correct control module for this vehicle is installed (part number and coding).

If the correct control modules are installed, check the CAN bus system.

Checking a "two-line bus system"

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.

Fig 2: Control Module 1 Not Communicating With Control Modules 2 And 3

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Example 1:

From the DTCs stored in the memories, you have determined that control module 1 is not communicating with control modules 2 and 3.

Control module	DTCs stored in DTC memories:
1	Missing signal from control module 2 Missing signal from control module 3
2	Missing signal from control module 1
3	Missing signal from control module 1

Switch ignition off.
Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Replace control module 1 if no malfunctions can be found in the bus wires.

Fig 3: Control Module 2 Not Communicating With Control Modules 1 And 3

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Example 2:

From the DTCs stored in the memories, you have determined that control module 2 is not communicating with control modules 1 and 3.

Control module	DTCs stored in DTC memories:
1	Missing signal from control module 2
2	Missing signal from control module 1 Missing signal from control module 3
3	Missing signal from control module 2

Switch ignition off.
Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Replace control module 2 if no malfunctions can be found in the bus wires.

Example 3:

Using the DTCs stored in the memories, you have determined that none of the control modules are sending or receiving signals.

Control module	DTCs stored in DTC memories:
1	e.g. powertrain data-BUS malfunctioning
2	e.g. powertrain data-BUS malfunctioning
3	e.g. powertrain data-BUS malfunctioning

Switch ignition off.

Fig 4: Control Modules Connected Across Bus Wires

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Disconnect the control modules connected across the bus wires and check for short circuits between the bus wires.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Fig 5: Checking Bus Wires For Short Circuit To B+ Or Ground

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Check the bus wires for short circuit to B+ or Ground (GND).

If a cause for the malfunction can not be determined, e.g. "powertrain data-BUS malfunctioning", check whether one of the control modules may be responsible for the DTC.

All control modules that use the CAN-bus are still disconnected. Ignition is switched off.

Connect one of the control modules.
Connect VAS 5051/5052 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, read the DTC memory of the control module just connected.

If the DTC "powertrain data-BUS malfunctioning" is displayed, replace the control module just connected.
If the DTC "powertrain data-BUS malfunctioning" is not displayed, connect the next control module and repeat the procedure.