Control Module: Testing and Inspection

Data Exchange Between Engine/ABS/Transmission Control Module, Checking


NOTE:
- The data exchange between the various control modules is carried out via a bus system.
- The term "Bus" refers to a system for transmitting and distributing data.
- The wires which connect the control modules and convey the data between them are called data wires.
- Data is transmitted via data wires in serial, i.e. in a specific order to the connected control modules.


Checking bus system
The DTC table indicates that the data exchange between the engine control module, ABS control module and transmission control module should be tested.
- Check Part No. and coding to make sure that vehicle is equipped with correct Engine Control Module (ECM), Transmission Control Module (TCM), ABS control module. (Display control module identification). If the correct control modules are installed:
- Check DTC memory of Transmission Control Module (TCM).
- Check DTC memory of ABS Control Module.

If a malfunction regarding "Data Bus" or "Communication" is displayed:
- Switch ignition off.







- Connect VAG1598/31 test box to wiring harness for engine control module. Do not connect to the engine control module itself. Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG1598/31 Test Box" Testing and Inspection
- Check data wiring according to wiring diagram between engine control module terminal 60 and 58 and transmission control module (if equipped) or ABS control module for open circuit and short circuit.

The following trouble shooting procedure is recommended if three or more control modules communicating via a "two-wire bus system".
- Read out malfunctions stored in the control modules.
This will help to identify a malfunction in the wiring.







Example 1
From the malfunctions present in the DTC memories, you can see that control module I has no connection to control modules 2 or 3.

Control module Stored malfunctions
in DTC memory:
1 - No message from control module 2
- No message from control module 3
2
- No message from control module 1
3 - No message from control module 1

- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check whether there is an open circuit in one of the bus wires

- If no malfunction can be identified in the bus wires replace control module 1.







Example 2
From the malfunctions present in the DTC memories, you can see that control module 2 has no connection to control modules 1 or 3.

Control Stored malfunctions
Module in DTC memory
1 - No message from control module 2
2 - No message from control module 1
- No message from control module 3
3 - No message from control module 2

- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check whether there is an open circuit in one of the bus wires
Locations
- If no malfunction can be identified in the bus wires replace control module 2.

Example 3
From the malfunctions present in the DTC memories, you can see that none of the control modules are able to transmit or receive signals.

Control Stored malfunctions
module in DTC memory:
1 - Data Bus Powertrain Malfunction
2 - Data Bus Powertrain Malfunction
3 - Data Bus Powertrain Malfunction


- Switch ignition off.







- Disconnect the control modules which are linked by the bus wires and check for a short circuit between the bus wires







- Check bus wires for short to B+ and short to Ground (GND)

If the cause of the malfunction "Data Bus Powertrain Malfunction" cannot be found in the data bus wires, check whether one of the control modules is causing the malfunction.

At this stage all the control modules which communicate via the CAN data bus are disconnected. The ignition is switched off.
- Connect one of the control modules.
- Connect VAG1551 scan tool. Switch ignition on and erase the DTC memory of the control module which has just been connected. End output from scan tool with function 06 "End Output."
- Switch ignition off and then on again.
- Leave ignition switched on for 10 seconds. Then check DTC memory of the control module that has just been connected, using the scan tool.
- If the malfunction "Data Bus Powertrain Malfunction" is now indicated, replace the control module which has just been connected.
- If malfunction "Data Bus Powertrain Malfunction" is not indicated, connect next control module, and repeat above procedure.