Data Exchange Between Engine Control Module and Other Control Modules With CAN-Bus Interface, Testing
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 wiring 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, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions and select vehicle system "01 - Engine electronics". Ignition must be switched on.
Display on VAS5051:
- Select diagnostic function "08 - read measured value block" in selection -1-.
Display on VAS5051:
1 - Enter display group. Max. input value = 255
NOTE: Measuring value blocks 125 and 126 indicate the participants in the powertrain data-BUS.
- Enter "125" in button field -2- for "display group number 125" and press Q button to confirm input.
Display on VAS5051:
- Check indications in display fields 1 through 4.
CAN-capable control modules connected to Engine Control Module (ECM) are indicated:
- No indication: Control module not CAN-capable
- Indication 1: CAN-capable control module is connected to data bus
- Indication 0: CAN-capable control module is not connected to data bus
- Press s button to change into display group 126.
- Check under display group 126 in same manner.
- Press <- button to end function "08 - Read measuring value block".
Display on VAS5051:
- Select diagnostic function "06 - end output" in selection -1 -.
Display on VAS5051:
- In selection -1-, press diagnostic function "00 - Check DTC memory - complete system".
- DTC memory of all OBD capable systems in 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".
Any system malfunctions that are stored will be displayed in sequence. The VAS5051 tester then sends the next address word.
If a malfunction related to the "powertrain databus" or the "CAN-bus" is indicated:
- Check whether 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 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 DTCs stored in memories of control modules.
NOTE: This analysis will help to locate the cause of the line malfunction.
Example 1
From the DTCs stored in the memories, it is 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 1
2 Missing signal from control module 3
3 Missing signal from control module 1
- Switch ignition off.
- Disconnect control modules connected across bus wires and check bus wires for an open circuit.
- Replace control module 1 if no malfunctions can be found in bus wires.
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.
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 control modules connected across bus wires and check bus wires for an open circuit.
- Replace control module 2 if no malfunctions can be found in bus wires.
Example 3
Using the DTCs stored in the memories, it is determined that none of the control modules are sending or receiving signals.
Control module DTCs stored in DTC memories:
1 Powertrain CAN-bus faulty
2 Powertrain CAN-bus faulty
3 Powertrain CAN-bus faulty
- Switch ignition off.
- Disconnect control modules connected across bus wires and check bus wires for a short circuit to B+ and Ground (GND).
If a cause cannot be determined for the DTC "Powertrain CAN-bus malfunction", check whether the DTC is caused by one of the control modules.
Requirement
- VAS5051 tester connected and vehicle On Board Diagnostic (OBD) selected, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions .
- All control modules that use the CAN-bus are still disconnected. Ignition is switched off.
- Connect one control module.
- Switch ignition on.
Display on VAS5051:
- Press relevant vehicle system in selection -1-.
- Check DTC memory of control module just connected and erase it.
- Click on <- button
- Select diagnostic function "06 - end output" in selection -1 -.
- Switch ignition off and on again.
- Leave ignition on for 10 seconds. Then, read DTC memory of control module just connected.
- If DTC "Powertrain CAN-bus malfunction" is displayed, replace control module just connected.
- If DTC "Powertrain CAN-bus malfunction" is not displayed, connect next control module and repeat procedure.