Fendt 06.1.17 – A039 - MFA (Multifunction Armrest): A039 - MFA, multifunction armrest: Speed preselection button 750 (or 540E) - Faulty button, signal fault.

The system is receiving an invalid electrical signal from the PTO speed preselection button on the armrest. The system detects that the button is either short-circuited, mechanically stuck in the depressed position, or has failed internally. As a safety consequence, the rear PTO speed cannot be modified or selected while this code is active.

• 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)
• Fendt 400 Vario (COM III)
• Fendt 700 Vario (COM III)
• Fendt 800 Vario (COM III)
• Fendt 900 Vario (COM III)

1. 1

   Inspect the 750 / 540E button on the armrest to see if it is physically jammed, sticky from spilled liquids, or held down by debris.

2. 2

   Attempt to clear the fault code from the terminal memory (simultaneously pressing keys D, B, and C) to see if it is a hard fault or a stored intermittent glitch.

3. 3

   Monitor the live state of the MFA buttons using FENDIAS diagnostic software.

4. 4

   Use a 160-pin adapter box to test the A039 MFA module's pinouts for continuity and proper voltage to rule out a wiring harness short.

1. 1

   Power Down

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

2. 2

   Disassemble the Armrest

   Carefully remove the retaining screws and plastic trim covers on the A039 multifunction armrest to access the internal button panels and circuit boards.

3. 3

   Inspect the Keypad

   Locate the PTO speed selection keypad block. Clean away any dust, dirt, or liquid residue that might be causing a short across the button's contacts.

4. 4

   Replace the Component

   If the button is physically broken or fails a multimeter continuity test, it must be replaced. You will likely need to replace the specific keypad sub-assembly rather than just the plastic button cap.

5. 5

   Reassembly

   Reconnect the ribbon cables/wiring harnesses to the MFA, ensuring all pins are seated correctly and not bent. Reinstall the armrest covers.

6. 6

   Test

   Reconnect the battery, turn on the ignition, and clear the fault codes. Test the PTO speed preselection to confirm the 750/540E speed engages properly and the code does not return.