Fendt 01.1.9C – Multifunction Armrest control module (A039 / A100): A039 - MFA, multifunction armrest: Communication fault with TMS button.

CAN bus communication failure specifically related to the TMS (Tractor Management System) button located on the joystick/armrest. Because the system cannot detect the status of the TMS button, the direct consequence is that the TMS is automatically switched off for safety and operational reasons.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• Fendt 900 Vario Series (COM III, SCR, and S4 generations, including 916, 920, 922, 924, 926, 927, 930, 933, 936, 939)
• Fendt 700 Vario Series (SCR generation)
• Fendt 300 Vario Series

1. 1

   Verify the Code: Confirm that 01.1.9C is active and that the TMS system is disabled.

2. 2

   Physical Inspection: Inspect the TMS button on the joystick for physical damage, sticking, or liquid ingress.

3. 3

   CAN Bus Wiring Check: Inspect the wiring harness and connectors leading from the MFA (A039/A100) to the main tractor CAN bus. Look for chafed wires, loose pins, or corrosion.

4. 4

   Diagnostic Tool Test: Use FENDIAS or SERDIA diagnostic software to monitor the CAN bus signals from the MFA. Check if the button press registers at all, or if the entire armrest module is experiencing intermittent offline states.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical shorts or static discharge to sensitive CAN components.

2. 2

   Access the MFA Internals

   Carefully remove the outer covers of the multifunction armrest to access the internal circuit boards and wiring for the joystick and buttons.

3. 3

   Inspect and Clean Connections

   Disconnect the ribbon cables or wiring connectors routing specifically to the TMS button. Clean them with electrical contact cleaner and reconnect securely.

4. 4

   Component Testing

   If the wiring is intact but the button fails to communicate, the fault likely lies within the button's microswitch or the armrest's internal circuit board (EMI filters and capacitors on these boards are known to occasionally short out due to static discharge).

5. 5

   Module Repair or Replacement

   Fendt does not typically sell the internal microswitches separately. If the internal board or button is faulty, you must either send the armrest control panel to an agricultural electronics specialist (such as Ilgenfritz Mechatronics) for board-level repair, or replace the MFA module/joystick entirely.

6. 6

   Reassembly and Clearing Codes

   Reassemble the armrest, reconnect the battery, and use the tractor's terminal to clear the stored 01.1.9C fault code. Test the TMS button to ensure functionality is restored.