Fendt 0B.1.25 – A050 - ECU, basic control unit: A050 - ECU, basic control unit; A039 - MFA, multifunction armrest. TEACH-IN. MFA does not report to bus.

The Multifunction Armrest (MFA) is failing to communicate with the tractor's basic control unit over the CAN bus network. Specifically, this communication loss is interrupting the "TEACH-IN" function (Fendt's Headland Management System / Variotronic TI).

• 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, SCR)
• Fendt 800 Vario (COM III, SCR)
• Fendt 900 Vario (COM III, SCR)
• Fendt 919
• Fendt 922
• Fendt 924
• Fendt 927
• Fendt 930
• Fendt 933
• Fendt 936
• Fendt 939

1. 1

   Inspect the wiring harness and connectors between the A039 Multifunction Armrest and the A050 Basic Control Unit. Look for chafed wires, pinched harnesses (especially near the seat/armrest pivot points), or loose connector pins.

2. 2

   Verify that the A039 MFA is receiving proper voltage. Check the A013 - PCB, microfuses, which supplies power to the tractor's electronics.

3. 3

   Look for related bus faults, such as 00.0.03 (Multifunction armrest bus fault, does not report to bus), which would confirm a total loss of communication from the armrest.

4. 4

   Use the Fendt 160-pin adapter box and a multimeter to test the pinouts at the A050 ECU and the A039 MFA to verify CAN High and CAN Low signal integrity.

1. 1

   Resolve Wiring Issues

   If a break or short is found in the CAN bus wiring between the armrest and the main cab harness, repair the wiring or replace the damaged harness section.

2. 2

   Component Replacement

   If the wiring, power, and grounds are intact, the fault lies internally within either the A039 MFA or the A050 ECU. Replace the faulty module.

3. 3

   EOL Programming

   If the A050 ECU or A039 MFA is replaced, End-of-Line (EOL) programming is strictly required. This must be done using the FENDIAS diagnostic software to pair the new module with the tractor's immobilizer and network.

4. 4

   Clear Fault Codes

   Canceling the fault code on the instrument panel only hides it from the display. Fault codes stored in the A050 ECU must be permanently deleted using the FENDIAS diagnostic software after the repair is complete.