Fendt 06.1.B8 – A039 - MFA (Multifunction Armrest): A039 - MFA, multifunction armrest. Button, speed selector 1000, REAR PTO. Communication fault.

The control system has lost communication with or is receiving an invalid signal from the button used to select the 1000 RPM speed for the rear Power Take-Off (PTO).

• 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 300 Vario (COM III / S4)
• Fendt 400 Vario (COM III)
• Fendt 700 Vario (COM III / SCR)
• Fendt 800 Vario (COM III / SCR)
• Fendt 900 Vario (COM III / SCR)

1. 1

   Check the physical condition of the Rear PTO 1000 RPM speed selector button on the armrest. Ensure it is not physically stuck, damaged, or contaminated with dirt/debris.

2. 2

   Inspect the internal wiring harness of the multifunction armrest. Look for pinched wires, loose connector pins, or corrosion that could interrupt the signal.

3. 3

   Test the A039 MFA module using a 160-pin adapter box to verify pinout signals and continuity.

4. 4

   Verify that the A039 MFA is properly communicating with the A050 Basic Control ECU via the CAN bus. If multiple buttons are failing simultaneously, the issue is likely the armrest's internal bus rather than a single switch.

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent electrical shorts during disassembly.

2. 2

   Access the MFA

   Carefully remove the top cover/bezel of the A039 Multifunction Armrest to expose the switch clusters and internal circuit boards.

3. 3

   Test/Replace the Switch

   Test the specific 1000 RPM PTO button for continuity. If the switch fails the continuity test, replace the individual switch or the switch cluster membrane (depending on the specific armrest revision).

4. 4

   Inspect the PCB

   If the switch is functional, inspect the MFA's internal printed circuit board (PCB) for burnt traces or moisture damage, which is a common cause of isolated communication faults.

5. 5

   Reassembly

   Reconnect all internal harnesses and reassemble the armrest housing.

6. 6

   Clear Codes & Calibrate

   Reconnect the battery. Turn the ignition on, access the tractor's diagnostic terminal, and clear the stored 06.1.B8 fault code. Test the rear PTO engagement at 1000 RPM to confirm the repair.