CLAAS Id78B7h / 78B7h (847) – Transmission module TR2 (A57-2): Communication loss with External function module EXT (A62)

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, causing the machine to automatically disconnect the differential lock.

• CLAAS Axion 800 Series (810, 830, 850, 870)
• CLAAS Axion 900 Series (920, 950)
• CLAAS Arion 400 Series (410, 430)
• CLAAS Arion 500 / 600 Series (510, 530, 550, 620, 640, 650)

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 continuity of the harnesses linking the TR2 module, the EXT module, and the CLAAS vehicle CAN bus network.

3. 3

   Test the CAN bus lines for any short-circuits (to 12V or to 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 calibrations between the modules using the CLAAS Diagnostic System (CDS) or METADIAG tool.

1. 1

   Safely secure the machine

   Turn off the ignition and disconnect the battery before probing sensitive CAN bus pins.

2. 2

   Inspect the CAN bus physical layer

   Locate the TR2 module (often located behind the driver's seat, described as an "Autotronic 5" type module with a 42-terminal connector) and the EXT module. Disconnect their harnesses and inspect the pins for corrosion, fretting, or pushed-out terminals.

3. 3

   Perform continuity and resistance tests

   Measure the resistance across the CAN High and CAN Low pins to ensure the network is intact and properly terminated (typically 60 ohms across the bus).

4. 4

   Restore power and test

   Reconnect the battery and turn the ignition on. Verify that both the TR2 and EXT modules are receiving steady 12V power and have clean grounds.

5. 5

   Clear and Retest

   Use the CLAAS Diagnostic System (CDS) to clear the fault memory. Run the tractor and initiate a CSM sequence to see if the differential lock disconnects and the code returns.

6. 6

   Module Replacement

   If wiring, power, and grounds are all verified as good, but the communication loss persists, the fault lies internally within one of the modules. Use diagnostic tool no. 60 05 033 249 to test and, if required, replace the TR2 (A57-2) module.