CLAAS Id78BBh / 78BBh (851) – TR3 (A57-3) Transmission Module: Communication loss with external function module EXT (A62)

The Transmission module TR3 (A57-3) has detected a communication loss with the external function module EXT (A62) during a CSM (CLAAS Sequence Management) sequence. As a safety and operational precaution, the rear power take-off (PTO) is automatically disconnected.

• CLAAS Axion 800 Series (e.g., 810, 840, 850)
• CLAAS Axion 900 Series (e.g., 920, 950)
• CLAAS Arion 400 Series (e.g., 410, 430)
• CLAAS Arion 500 / 600 Series (e.g., 510, 640)

1. 1

   Attempt a manual reset of the CLAAS Sequence Management (CSM) if the system does not initialize after 20 seconds

2. 2

   Check the operational status of the TR3 transmission module (A57-3) and the external function module EXT (A62)

3. 3

   Check the CLAAS vehicle CAN bus network for communication integrity between the TR3 and EXT modules

4. 4

   Inspect the connectors and continuity of the harnesses linking the TR3, EXT, and CAN bus components for short-circuits (to 12V or ground) or open circuits

5. 5

   Check the power supply sources for both modules, including fuses, power supply lines, and grounds

1. 1

   Initial Reset

   Turn off the ignition, wait for the system to power down completely, and restart the tractor. Attempt to reset the CSM sequence.

2. 2

   Inspect Physical Connections

   Locate the TR3 (A57-3) transmission module (often located behind the driver's seat, utilizing a 42-terminal connector) and the EXT (A62) module. Disconnect and inspect the harness connectors for corrosion, pushed pins, or moisture.

3. 3

   Test Wiring

   Using a multimeter, test the CAN High and CAN Low lines between the TR3 module, the EXT module, and the CAN network communication module (BDG A103) for continuity and proper resistance (typically 60 ohms across the CAN network).

4. 4

   Repair Wiring

   If a short or open circuit is found in the harness, repair or replace the damaged section of the wiring.

5. 5

   Module Replacement

   If the wiring, power, and grounds are all intact and the communication loss persists, the fault lies within the internal CAN transceivers of one of the modules. Replace the faulty module (TR3 or EXT) and perform any required programming/calibration to match the tractor's configuration.