TCM and CAN-Capable Control Module Data Exchange, Checking
TCM and CAN-Capable Control Module Data Exchange, Checking
• The exchange of data between the individual control modules is carried out by means of a bus system.
• "CAN-bus" describes a system to carry and distribute data.
• The wiring connections between the control modules, over which the data are transmitted, are described as data lines.
• Data are transmitted serially, that means in sequence, over these data lines to the attached control modules (e.g. engine RPM, accelerator pedal position).
Checking Bus System
In the DTC Chart you were instructed to verify the exchange of data between the Transmission Control Module (TCM) and CAN-capable control modules.
- Connect Vehicle Diagnosis, Measurement and Information System (VAS5051) => [ VAS 5051, Connecting and Selecting Functions ] VAS 5051, Connecting and Selecting Functions and in selection touch vehicle system "02 - Transmission Electronics". Ignition must be switched ON.
Display on (VAS5051):
- In selection touch - 1 - diagnostic function " 08 - Read Measured Value Block".
Display on (VAS5051):
1. Enter display group
• Measured Value Block 125 shows the participants on the data BUS drive.
- On keypad enter - 2 - "125" for " Display Group Number 125" and confirm by touching Q button.
Display on (VAS5051):
- Check display in display fields - 1 - to - 3 -.
The display shows the control modules which are CAN-capable with the Engine Control Module (ECM):
• Display 1: CAN capable control module is participant on the data bus
• Display 0 or no display: CAN-capable control module is not participant on the data bus or not CAN-capable
- End function "08 - Read Measured Value Block" by touching arrow button.
- Touch "06 - End output".
Display on (VAS5051):
- In selection - 1 - touch diagnostic function " 00 - Scan DTC memory - complete system".
• Now the DTC memory of all systems in the vehicle capable of self diagnosis is scanned.
If a control module responds and identifies itself, the number of stored trouble codes or "No trouble code" is displayed.
Any stored DTCs in a system are shown in sequence. Then the ( VAS5051) sends the next address word.
If a DTC referring to "Data bus drive..." or "...CAN-bus" is displayed:
- Check whether correct Engine Control Module (ECM) and other CAN-capable control modules have been installed (Part No. and Code).
If the correct control modules have been installed:
- Check whether multiple connectors for control modules are fully seated.
If the multiple connectors are fully seated.
- Check CAN-bus system.
Communication takes Place Between Two or more Control Modules over a Dual-Wire-Bus System
- Analyze DTCs stored in control modules.
• The analysis helps you to pinpoint the wiring fault.
Example 1:
Based on the DTCs entered in the DTC memories, you can see that control module 1 is not connected to control modules 2 and 3.
- Switch ignition OFF.
- Disconnect control modules connected by bus wiring and check whether one bus wiring connection has an open circuit.
- If no malfunction is found in bus wiring, replace control module 1.
Example 2:
Based on the DTCs entered in the DTC memories, you can see that control module 2 is not connected to control modules 1 and 3.
- Switch ignition OFF.
- Disconnect control modules connected by bus wiring and check whether one of bus wiring connections has an open circuit.
- If no malfunction is found in bus wiring, replace control module 2.
Example 3:
Based on the DTCs entered in the DTC memory, you see that no transmission or reception activity is possible in any of the control modules.
- Switch ignition OFF.
- Disconnect control modules connected by bus wiring and inspect bus wiring for a short circuit to B+ and to ground.
If you are unable to determine any cause in the bus wiring for the DTC "Data bus drive faulty", check to see whether one of the control modules is responsible for this DTC.
Test Prerequisite
• Vehicle Diagnosis, Measurement and Information System (VAS5051) connected and Vehicle Self Diagnosis selected => [ VAS 5051, Connecting and Selecting Functions ] VAS 5051, Connecting and Selecting Functions.
All the control modules which use the CAN-bus for communication are disconnected. The ignition is switched OFF.
- Connect one control module.
Display on (VAS5051):
- Switch ignition ON.
- Touch appropriate vehicle system in Display - 1 -.
- Read DTC memory of control module just connected and delete it.
- Touch > button.
- In display touch - 1 - diagnostic function " 06 - End output".
- Switch ignition OFF and ON again.
- Leave ignition switched ON for 10 seconds. Then, using scan tool, read DTC memory of control module just connected.
- If DTC "Data bus drive faulty" is read, control module just connected must be replaced.
- If DTC "Data bus drive not faulty" is not read, connect next control module and repeat procedure.