Fendt 01.1.9B – A039 - MFA (Multifunction Armrest) / A100 - MFA: A039 - MFA, multifunction armrest: Communication fault with cruise control button MAX.

The control unit is not receiving the expected CAN bus signal from the 'MAX' cruise control button located on the Vario joystick. As a direct safety and operational consequence, the Tractor Management System (TMS) is automatically switched off and will remain disabled until the next trouble-free engine start.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• 300 Vario (COM III)
• 400 Vario (COM III)
• 700 Vario (COM III, SCR)
• 800 Vario (COM III, SCR)
• 900 Vario (COM III, SCR)

1. 1

   Inspect the cruise control 'MAX' button on the Vario joystick for physical damage, sticking, or debris preventing the microswitch from engaging.

2. 2

   Restart the tractor to see if the fault clears, as the TMS system disables itself until the next cold start.

3. 3

   Inspect the internal wiring harness and connectors within the armrest connecting the joystick to the MFA control board for pin corrosion, loose connections, or wire chafing.

4. 4

   Connect the FENDIAS diagnostic software to monitor the live state of the joystick buttons and check if the 'MAX' button registers or shows an open/short circuit.

5. 5

   Verify the CAN bus communication lines to the MFA module.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent electrical shorts during disassembly.

2. 2

   Access the MFA

   Carefully remove the covers of the multifunction armrest to access the base of the Vario joystick and the MFA control board.

3. 3

   Disconnect the Joystick

   Unplug the joystick's electrical harness from the MFA module.

4. 4

   Component Repair/Replacement

   If the diagnostic tests point to a failed internal microswitch or joystick circuit board, the joystick/drive lever must be repaired or replaced. If the issue is isolated to the MFA control board itself failing to process the CAN signal, the armrest module must be replaced.

5. 5

   Reassembly

   Install the repaired/new joystick or armrest module. Route the wiring harness exactly as it was from the factory to prevent pinching when the armrest is adjusted.

6. 6

   Re-energize

   Reconnect the battery.

7. 7

   Calibration (If Applicable)

   Connect the FENDIAS diagnostic tool. If a new MFA module or joystick was installed, you may need to perform an End-of-Line (EOL) programming or calibration to ensure it communicates properly with the basic control unit (A050).

8. 8

   Testing

   Clear the stored fault codes and test the cruise control MAX button and TMS functionality during a test drive.