Fendt 05.1.31 – A039 - MFA (Multifunction Armrest) / A050 - ECU, basic control unit: A039 - MFA, multifunction armrest 4WD 100% button - Sensor faulty / Signal fault

The system has detected an electrical issue (such as a short circuit, open circuit, or a physically stuck switch) with the button used to manually engage 100% Four-Wheel Drive on the multifunction armrest. As a result, the manual 100% 4WD button is disabled, and the tractor will only allow the use of the '4WD automatic mode' until the fault is resolved.

• 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 200 V/F/P Vario series
• Fendt 300 Vario series
• Fendt 400 Vario series
• Fendt 700 Vario series
• Fendt 800 Vario series
• Fendt 900 Vario series (916, 922, 924, 927, 930, 933, 936)

1. 1

   Inspect the 4WD 100% button on the multifunction armrest for physical damage, sticking, or debris/liquid ingress.

2. 2

   Inspect the wiring harness and connectors between the A039 Multifunction Armrest and the A050 Basic Control Unit for pinched wires, corrosion, or loose pins.

3. 3

   Test the A039 MFA using a 160-pin adapter box or FENDIAS diagnostic software to monitor the live state of the 4WD button.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical spikes during module removal.

2. 2

   Access the Armrest

   Remove the protective covers on the right-hand driver seat console (often a Grammer-built seat console) to expose the underside of the A039 Multifunction Armrest.

3. 3

   Clean the Contacts

   If the button is simply sticking due to dirt, attempt to clean the keypad area with electrical contact cleaner.

4. 4

   Replace the Component

   If the button has failed internally, the specific keypad module or the entire A039 Multifunction Armrest must be replaced. Disconnect the main harness from the MFA, unbolt the armrest module from the seat console, and install the replacement unit.

5. 5

   Reassembly and Power-Up

   Reconnect the wiring harness, reattach the console covers, and reconnect the battery.

6. 6

   Calibration / EOL Programming

   If a completely new A039 MFA is installed, perform End-of-Line (EOL) programming via the FENDIAS dealer tool so that the new armrest can report correctly to the CAN bus and the A050 ECU. Clear the stored 05.1.31 fault code.