Data Exchange Between ECM and Other Can-Control Modules
Data Exchange Between Engine Control Module And Other CAN-control Modules, Checking
NOTE:
- Data is exchanged between individual control modules by means of a bus system.
- "CAN bus" is used to describe a system that transports and distributes data.
- The wires between the control modules that are used to transfer the data are known as signal wires.
- Data is transmitted via data wires in sequence, i.e. in a specific order to the connected control modules (e.g. engine rpm and accelerator pedal position).
Testing the bus system
The DTC table instructed you to check the data exchange between the engine control module and CAN-compatible control modules.
- Connect testing and information system VAS 5051 and select vehicle system "01 - Engine electronics" in selection. Ignition must be switched on. Connecting VAS 5051 Scan Tool
Display on VAS 5051:
- Under -1- select diagnostic function "08 - Read measured value block".
Display on VAS 5051:
1 - Enter display group.
NOTE: The measured value blocks 125 and 126 indicate CAN drive users.
- Enter "125" for "display group number 125" in zone -2- and confirm entry by pressing -Q- button.
Display on VAS 5051:
- Check displays in display zones -1- to -4-.
- CAN-compatible control modules are displayed with the engine control module:
- No display: Engine control module not CAN-compatible.
- Display 1: CAN-compatible control module is a data bus user.
- Display 0: CAN able control module is not user of the Databus.
- To change to display group 126, press the s button.
- Check same way with display group number 126.
- Exit function "08 - Read measured value block" by pressing <- button.
Display on VAS 5051:
- Under -1- select diagnostic function "06 - End output".
Display on VAS 5051:
- Under -1- select diagnostic function "00 - check DTC memory - whole system".
- The DTC memory is then checked for all systems in the vehicle which are capable of self-diagnosis.
If a control module answers with its identification, the number of DTCs stored or "No malfunction detected" appears on the display.
Any system DTCs that are stored are displayed successively. The VAS 5051 will then transmit the next address word.
If a DTC is displayed relating to "Data bus drive ..." or "... CAN bus":
- Check that engine control module and other CAN-compatible control modules installed are suitable for this vehicle (part no. and code).
If the correct control modules are installed:
- Check that multiple connectors for control modules are properly seated.
If the multi-pin connectors are firmly seated:
- Check CAN bus system.
Checking a "two-wire bus system"
The communication between three or more control modules is carried out over a " twoline bus system".
- Evaluate DTCs stored in control modules.
NOTE: This helps to localize line malfunctions.
Example 1:
- The DTCs stored in the DTC memories indicate that the control module 1 does not communicate with control modules 2 and 3.
Control module DTCs stored 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 linked to one another via bus wires and check whether there is an open circuit between bus wires.
- If no DTC can be detected in bus lines exchange control module 1.
Example 2:
- The DTCs stored in the DTC memories indicate that the control module 2 does not communicate with control modules 1 and 3.
Control module DTCs stored 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 linked to one another via bus wires and check whether there is an open circuit between bus wires.
- If no DTC can be detected in bus lines exchange control module 2.
Example 3:
- The DTCs stored in the DTC memories indicate that sending or receiving is not possible in any of the control modules.
Control module DTCs stored in DTC memory
1 - Data bus drive malfunction
2 - Data bus drive malfunction
3 - Data bus drive malfunction
- Switch ignition off.
- Disconnect control modules that are linked to one another by bus wires and check bus wires for short circuits to positive and Ground.
If cause of DTC "Data bus drive faulty" cannot be found in bus lines check whether one of the control modules is responsible for the malfunction.
Test requirements:
- Vehicle diagnosis, measurement and information system VAS 5051 connected and vehicle On Board Diagnosis selected. Connecting VAS 5051 Scan Tool
All the control modules that communicate via the CAN data bus are still disconnected. Ignition is switched off.
- Connect one control module.
Display on VAS 5051:
- Switch ignition on.
- Select applicable vehicle system under -1-.
- Check and erase DTC memory in control module which has just been connected.
- Press <- button.
- Under -1- select diagnostic function "06 - End output".
- Switch ignition off and then on again.
- Leave ignition switched on for 10 seconds. Then check DTC memory of control module that has just been connected, using scan tool.
- If DTC "Data bus drive faulty" is now indicated, replace control module which has just been connected.
- If DTC "Signal wire defective" is not read out, connect next control module and repeat procedure.