Fendt 04.1.70 – Basic Control Unit ECU (A050) / MFA (Multifunction Armrest) module (A039 or A100): A039 (or A100) - MFA, multifunction armrest. Cruise control button, C1. Faulty button, Signal fault.

The system has detected an electrical signal fault (such as an open circuit, short, or implausible continuous signal) originating from the C1 cruise control button located on the tractor's main drive joystick. As a result, the tractor's Cruise Control 1 function cannot be activated.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• 300 Vario series
• 400 Vario series
• 700 Vario series
• 800 Vario series
• 900 Vario series
• 1000 Vario series

1. 1

   Inspect the C1 button on the Vario drive lever (joystick) for physical damage, sticking, or dirt/debris lodged around the switch housing that might be holding the button down.

2. 2

   Check for related codes (e.g., 04.1.71 for the C2 button or 01.1.7B for the MAX button). If multiple buttons are failing simultaneously, the issue is likely a failure of the joystick's internal CAN circuit board or the main wiring harness.

3. 3

   Check the wiring harness and connectors linking the joystick to the main MFA armrest control board for pinched wires, pin damage, or loose connections.

1. 1

   Power Down

   Turn off the ignition and disconnect the battery before servicing the armrest electronics to prevent short circuits.

2. 2

   Assess the Damage

   If only the external plastic button cap is cracked or missing, you can carefully pry out the remnants and snap an aftermarket replacement button into the joystick housing. If the button physically clicks but does not register, the internal foil membrane keypad or microswitch has failed.

3. 3

   Disassembly

   Remove the screws securing the Vario joystick handle halves or the MFA control panel faceplate to access the internal circuit board.

4. 4

   Component Replacement/Repair

   Option A (OEM Route): Replace the entire Vario joystick assembly or the specific button keypad plate. Option B (Repair Service): Use specialized agricultural electronics repair shops (such as Ilgenfritz Mechatronics) to replace the defective foil buttons/membrane keypads and test the joystick's CAN circuit board.

5. 5

   Reassembly

   Install the new or repaired joystick/panel, reconnect the wiring harnesses, and reassemble the armrest.

6. 6

   Calibration/Clearing

   Restore battery power, turn on the ignition, and clear the fault codes via the Vario terminal. Test the C1 button to ensure the cruise control speed can be set and activated.