Fendt 06.1.B6 – A039 - MFA (Multifunction Armrest) / A100 - MFA: Communication fault: Button, speed selector 540, REAR PTO

The tractor's electronic system has lost communication with or is receiving an invalid signal from the button used to select the 540 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
• Fendt 400 Vario
• Fendt 700 Vario
• Fendt 800 Vario
• Fendt 900 Vario
• 916
• 920
• 922
• 924
• 927
• 930
• 933
• 936

1. 1

   Physical Inspection: Check the 540 RPM rear PTO button on the armrest for physical damage, sticking, or liquid intrusion (a common cause of membrane switch failure).

2. 2

   System-Wide Bus Check: Look for accompanying fault codes (such as 00.0.03 - A039 Multifunction armrest bus fault) which would indicate a broader CAN bus failure rather than an isolated button issue.

3. 3

   Wiring and Connector Test: Inspect the main wiring harness connecting the A039 armrest to the tractor. Check connector X1401 (which links the MFA to the A050 Basic Control Unit) for loose pins or corrosion.

4. 4

   Pin-Out Testing: Use the official 160-pin adapter box to test the A039 multifunction armrest's electrical inputs and outputs to verify if the signal is leaving the armrest.

5. 5

   Emergency Override Test: Verify if the PTO can still be engaged using the emergency PTO button in the cab. If it can, the issue is strictly isolated to the armrest button/communication, ruling out mechanical PTO failure.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical shorts while working on the CAN bus components.

2. 2

   Access the MFA

   Carefully remove the retaining screws on the underside of the A039 Multifunction Armrest to lift the top control panel/keypad cover.

3. 3

   Inspect Internal Connections

   Check the internal ribbon cables connecting the PTO speed selector keypad to the armrest's main circuit board. Reseat the ribbon cable, as vibration can sometimes cause communication faults.

4. 4

   Clean Contacts

   Use a dedicated electronic contact cleaner on the board connections.

5. 5

   Replace Component

   If the button membrane is internally shorted or the board has failed (confirming the communication fault), replace the affected keypad module or the complete upper armrest control board.

6. 6

   Reassembly and Calibration

   Reassemble the armrest and reconnect the battery. Connect the FENDIAS diagnostic tool to clear the stored 06.1.B6 fault code. If a new armrest module was installed, you must perform an End-of-Line (EOL) programming/calibration so the A050 ECU recognizes the new module.