Fendt 18.1.01 – A039 (or A100) Multifunction Armrest (MFA) / A050 Basic Control Unit (EXT): A039 - MFA, multifunction armrest. Auto-Guide partial activation button. Partial activation button in MFA faulty, Signal fault.

The basic control unit has detected a signal fault (such as a short circuit, open circuit, or a stuck switch) specifically originating from the Auto-Guide (or VarioGuide) partial activation button located on the tractor's multifunction armrest.

• 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, S4)
• Fendt 800 Vario (COM III, SCR, S4)
• Fendt 900 Vario (COM III, SCR, S4)

1. 1

   Inspect the Auto-Guide partial activation button on the MFA joystick/armrest for physical damage, sticking, or debris (like dirt or spilled liquids).

2. 2

   Verify the wiring harness and connectors between the A039/A100 MFA and the main tractor harness for CAN bus communication errors.

3. 3

   Use FENDIAS diagnostic software or a 160-pin adapter box to monitor the live signal state of the Auto-Guide button (check if it reads as permanently active or completely unresponsive).

4. 4

   Attempt to clear the fault code via the tractor terminal and restart the tractor to see if the code returns as an active fault.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the tractor's battery to prevent electrical shorts while working on the armrest.

2. 2

   Disassemble the MFA

   Carefully remove the top cover/plate of the multifunction armrest to access the internal switches and the joystick assembly.

3. 3

   Test the Switch

   Locate the specific micro-switch for the Auto-Guide partial activation button. Test it for continuity using a multimeter.

4. 4

   Clean or Replace Component

   If the button is simply stuck due to debris, clean the contact area with electrical contact cleaner. If the micro-switch fails the continuity test, the switch plate or the individual button mechanism must be replaced.

5. 5

   Replace Armrest Plate (if necessary)

   If the internal circuit board of the MFA is damaged and cannot process the button signal, the MFA contact plate or the entire armrest assembly will need to be replaced.

6. 6

   Reassembly & Calibration

   Reassemble the armrest, reconnect the battery, and turn on the ignition.

7. 7

   Clear Codes

   Use the terminal or FENDIAS to clear the stored 18.1.01 fault code. Test the Auto-Guide partial activation function to confirm the repair is successful.