Fendt 0F.1.2A – A039 - MFA (Multifunction Armrest): A039 - MFA, multifunction armrest. Button, hydraulic circuit 4.

The system has detected an electrical fault on the button that controls hydraulic circuit 4, located on the multifunction armrest (joystick). This is typically caused by a broken signal wire, a short circuit, or a physically stuck/defective microswitch. As a safety consequence, the button is rendered inoperable and the valve is locked until the next trouble-free cold start.

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• 936 Vario COM III
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• Fendt 400 Vario (COM III)
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• Fendt 900 Vario (COM III)

1. 1

   Inspect the hydraulic circuit 4 button on the joystick to see if it is physically stuck, sticking due to dirt/debris, or double-actuating.

2. 2

   Test the signal voltage for the 'Hydraulic circuit 4' button. When not operated, it should read 0 VDC. When operated with the engine running, it should read 14 VDC.

3. 3

   Check the internal wiring harness and connectors between the joystick buttons and the main A039 MFA control board for broken wires or pinched lines (especially inside the joystick pivot point).

4. 4

   Perform a trouble-free cold start to see if the fault clears, as the system locks the valve when this fault is triggered.

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent short circuits while working on the armrest electronics.

2. 2

   Disassemble the Joystick

   Carefully remove the covers of the multifunction armrest to access the joystick drive lever's internal wiring and button board.

3. 3

   Inspect and Repair Wiring

   Look for chafed or broken wires at the base of the joystick where it pivots. If a wire is broken, splice and repair the connection.

4. 4

   Test/Replace the Button

   If the wiring is intact but the button fails the voltage test (does not switch to 14 VDC), the microswitch on the board is defective.

5. 5

   Component Replacement

   If the button cannot be individually desoldered/replaced, the joystick drive lever assembly must be replaced, or the unit must be sent to an agricultural electronics repair specialist (such as Ilgenfritz Mechatronics).

6. 6

   Reassembly and Calibration

   Reassemble the armrest, reconnect the battery, and perform a cold start. Verify that the fault code is cleared and test the operation of hydraulic circuit 4.