CLAAS Id78D2h / 78D2h – EXT (A62) - External Function Module: CAN "Driver sitting" message is not received by the EXT (A62) external function module, or the received value is invalid

The tractor's network has lost the signal that confirms the operator is sitting in the driver's seat, which is a critical safety parameter for transmission and PTO operations.

• CLAAS Axion 800 Series (810, 820, 830, 840, 850)
• CLAAS Axion 900 Series (920, 930, 940, 950)
• CLAAS Arion 500 / 600 Series (510–540, 610–640)

1. 1

   Verify the physical operator presence switch (seat contact switch) located in the driver's seat is not physically stuck, disconnected, or packed with debris.

2. 2

   Inspect the connectors and pins on the TR2 transmission module (A57-2), the BDG communication module (A103), and the EXT external function module (A62).

3. 3

   Check the continuity of the harnesses linking the seat switch to the CAN network.

4. 4

   Test the CLAAS vehicle CAN bus for short-circuits to 12V or ground, and check for open circuits.

5. 5

   Check the energy sources (fuses, power supply, and ground) for the A62, A103, and A57-2 modules.

1. 1

   Test the Seat Contact Switch

   Disconnect the seat switch harness under the driver's seat. Use a multimeter to test for continuity. The switch should close (show continuity) when weight is applied to the seat and open when empty. If it fails this test, replace the seat switch.

2. 2

   Inspect Wiring

   If the switch works, trace the wiring from the seat base to the main cab harness. Look for pinched wires or chafing, which is common under suspension seats. Repair any damaged wires.

3. 3

   Check Module Connections

   Locate the EXT (A62) and BDG (A103) modules. Disconnect their main harness plugs, inspect for bent pins, moisture, or corrosion, and clean with contact cleaner. Reconnect securely.

4. 4

   Clear Codes and Retest

   Turn the ignition on and check the Cebis terminal. Sit in the seat and observe if the "Driver sitting" status updates.

5. 5

   Module Replacement (Worst Case)

   If the wiring and switch are perfect but the EXT module still cannot see the CAN message, the TR2, BDG, or EXT module may have an internal CAN transceiver failure. Module replacement will require the CLAAS Diagnostic System (CDS) to flash and calibrate the new unit.