CLAAS Id78B0h / 78B0h (840) – TR2 Transmission Module: Communication loss between TR2 Transmission module and EXT External function module

The Transmission module TR2 (A57-2) has detected a communication loss with the External function module EXT (A62) during a CSM (CLAAS Sequence Management) sequence. As a system response to this communication failure, the gear selection command is automatically disconnected.

• Axion 810
• Axion 820
• Axion 830
• Axion 840
• Axion 850
• Axion 920
• Axion 930
• Axion 940
• Axion 950
• Arion 610
• Arion 620
• Arion 630
• Arion 640
• Arion 650
• Arion 510
• Arion 520
• Arion 530
• Arion 540
• Arion 550
• Arion 410
• Arion 420
• Arion 430

1. 1

   Check the TR2 transmission module (A57-2) and the external function module EXT (A62) for signs of physical damage or water ingress

2. 2

   Check the connectors and the continuity of the wiring harnesses linking the TR2 and EXT modules

3. 3

   Test the CAN bus network for any short-circuits (to 12V or ground) or open circuits

4. 4

   Check the sources of energy for both modules, including all relevant fuses, power supply lines, and ground connections

5. 5

   Check the compatibility of the program versions, settings, and calibration between the modules using the CLAAS Diagnostic System (CDS)

1. 1

   Initial Reset

   Clear the fault codes and attempt to relaunch the CSM sequence to see if the communication loss was a momentary glitch.

2. 2

   Visual Inspection

   Inspect the wiring harness running between the transmission control unit (usually located behind the driver's seat) and the external functions module. Look for chafed wires or loose connector pins.

3. 3

   Electrical Testing

   Using a multimeter, verify the CAN High and CAN Low lines between the TR2 (A57-2) and EXT (A62) modules. Ensure the CAN bus terminating resistors are intact.

4. 4

   Power Supply Test

   Verify that both the TR2 and EXT modules are receiving stable 12V power and have clean grounds.

5. 5

   Software Update

   If the wiring is fully intact, connect the CLAAS Diagnostic System (CDS) to verify if a software update or parameter reset is required for the TR2 or EXT modules.

6. 6

   Module Replacement

   If all wiring, power, and software checks pass but the communication loss persists, replace the faulty module (starting with the EXT module or TR2 module based on CDS live data testing).