Data Transfer Between ECM & CAN Capable Control Modules Check
Data Transfer Between Engine Control Module (ECM) And CAN Capable 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 (i.e. engine speed, accelerator position).
Checking bus system
The DTC table suggested checking the data exchange between the Engine Control Module (ECM) and CAN capable control modules.
- Connect VAS5051 tester or VAG1551 scan tool and select the control module for engine electronics using "address word" 01. Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAS5051/VAG1551 Scan Tool" Testing and Inspection
Ignition must remain switched on for this.
When indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read Measuring Value Block" and press -Q- button to confirm input.
When indicated on display:
Read Measuring Value Block Q
Input display group number XXX
- Press buttons -1-, -2- and -5- to select "display group number 125" and press -Q- button to confirm input.
- Check indications in display fields 1 through 4.
CAN capable control modules connected to the Engine Control Module (ECM) are indicated:
- No indication: Control module no CAN capable
- Indication 1: CAN capable control module is connected to database
- Indication 0: CAN capable control module is not connected to database
NOTE: Measuring value blocks 725 and 726 indicate the components that are part of the powertrain data bus.
- Press -> button.
When indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -6- to select "End output" and press -Q- button to confirm input.
When indicated on display:
Rapid data transfer HELP
Select function XX
- Press button 0- twice to select "Automatic test sequence", address word 00. Press -Q- button to confirm input.
- DTC memory of all OBD capable systems in the vehicle will be checked.
When a control module responds with its identification, the display indicates the number of stored errors or indicates "no malfunctions recognized".
DTCs stored in the system are indicated in sequence and printed out. Then the VAG1551 scan tool sends the next address word.
V.A.G - ON BOARD DIAGNOSTIC HELP
1 - Rapid data transfer*
2 - Blink code output*
The automatic test sequence is over when the following indication appears on the display:
If a malfunction related to the "powertrain database" or the "CAN-bus" is indicated:
- Check whether the Engine Control Module (ECM) and other CAN capable control modules installed are appropriate for this vehicle (part no. and coding).
If the correct control modules are installed:
- Check to be sure the multi-pin connectors of the control modules are securely connected.
If multi-pin connectors are properly secured:
- Check 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.
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.
- Switch ignition off.
- Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.
- Replace control module 1 if no malfunctions can be found in the bus wires.
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.
- Switch ignition off.
- Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.
- 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.
- Switch ignition off.
- Disconnect the control modules connected across the bus wires and check bus wires for a short circuit to B+ and Ground (GND).
If you cannot determine a cause for the DTC "Powertrain database malfunction, check whether the DTC is caused by one of the control modules.
All control modules that use the CAN-bus are still disconnected. 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 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 you just connected.
- If the DTC "Powertrain database malfunction" is displayed, replace the control module you just connected.
- If the DTC "Powertrain database malfunction" is not displayed, connect the next control module and repeat the procedure.