Data Exchange Between Control Modules, Checking
Data Exchange Between Engine Control Module And Connected Control Modules, Checking
NOTE:
- Data is exchanged between the individual control modules by means of a bus system.
- "CAN bus" is the term used to describe a data transfer and distribution system.
- The wires between the control modules on which data are transmitted are referred to as signal wires.
- Data is transmitted serially along these signal wires to the connected control modules (e.g. engine speed, accelerator pedal position).
Checking bus system
If the fault table indicates that the data exchange between the engine control module and the control modules with CAN capability is to be checked:
- Check for proper connection of multi-pin connectors of control modules.
- Connect vehicle diagnostic, testing and information system VAS 5051 and select vehicle system "01 - Engine electronics" from list. Ignition must be on. Connecting VAS 5051 Scan Tool
Indicated on VAS 5051:
- From list -1- select diagnostic function "08 - Reading measured value block".
Indicated on VAS 5051:
1 Enter display group
NOTE: Measured value blocks 125 and 126 indicate drive train data bus users.
- Use keypad -2- to enter "125" for "Display group number 125" and confirm by touching Q key.
Indicated on VAS 5051:
- Check displays in zones -1- to -4-.
Display shows control modules capable of CAN communication with engine control module:
- No display: Control module has no CAN capability
- Display 1: Control module with CAN capability is data bus user
- Display 0: Control module with CAN capability is not data bus user
- Touch s key to switch to display group 126.
- Check in same way under display group number 126 (this display group may be completely blank).
- Terminate function "08 - Reading measured value block" by touching <- key.
Indicated on VAS 5051:
- From list -1- select diagnostic function "06 - End of output".
Indicated on VAS 5051:
- From list -1- select diagnostic function "00 - Interrogating fault memory - entire system".
- Fault memories of all vehicle systems with self-diagnosis capability are interrogated
If a control module responds with its identification, the number of stored faults or "No faults detected" appears on the display.
Any stored system faults are consecutively displayed. VAS 5051 then transmits the next address word.
If a fault relating to "Drive train data bus..." or "...CAN bus" is displayed:
If correct control modules are installed:
- Check that correct engine control module for this vehicle and other control modules with CAN capability have been installed (Part no. and code).
If correct control modules are installed:
- Check for proper connection of multi-pin connectors of control modules.
If multi-pin connectors are properly attached:
- Check CAN bus system.
Checking "two-wire bus system"
Communication is implemented between three or more control modules by way of a "two-wire bus system".
- Assess faults stored in control modules.
NOTE: Assessment helps to localize wiring fault.
Example 1:
Faults entered in fault memories reveal that control module 1 has no link
with control modules 2 and 3.
Control module Faults entered in fault 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 off ignition.
- Disconnect control modules linked by bus wires and examine bus wires for open circuit.
- Replace control module 1 if no faults are found in bus wires.
Example 2:
Faults entered in fault memories reveal that control module 2 has no link
with control modules 1 and 3.
Control module Faults entered in fault 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 off ignition.
- Disconnect control modules linked by bus wires and examine bus wires for open circuit.
- Replace control module 2 if no faults are found in bus wires.
Example 3:
Faults entered in fault memory reveal that none of the control modules
can transmit or receive.
Control module Faults entered in fault memory
1 Drive train data bus faulty
2 Drive train data bus faulty
3 Drive train data bus faulty
- Switch off ignition.
- Disconnect control modules linked by bus wires and examine bus wires for short to positive and Ground.
If cause of "Drive train data bus faulty" fault is not found in bus wires, check whether one of the control modules is responsible for the problem.
Requirements
- Vehicle diagnostic, testing and information system VAS 5051 connected up and vehicle self-diagnosis selected
- All control modules using CAN bus for communication still disconnected; ignition off
- Connect one control module.
Indicated on VAS 5051:
- Switch on ignition.
- From list -1- select appropriate vehicle system.
- Interrogate and erase fault memory of control module just connected.
- Touch <- key.
- From list -1- select diagnostic function "06 - End of output".
- Switch ignition off and on again.
- Leave ignition switched on for 10 seconds. Then use Scan Tool to read out fault memory of control module just connected.
- If fault "Drive train data bus faulty" is read, replace control module just connected.
- If fault "Drive train data bus faulty" is not read, connect next control module and repeat sequence.