Fendt 04.1.23 – A050 - ECU, basic control unit: Joystick signal "Tempomat cruise control ON" faulty.

The system has detected an electrical signal fault originating from the cruise control "ON" button located on the Vario joystick. When this fault is active, the Tractor Management System (TMS) may switch off or restrict functions, but continuation in emergency mode is possible.

• 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)
• FENDT 800 Vario (COM III)
• FENDT 900 Vario (COM III)

1. 1

   Physically inspect the 'Tempomat cruise control ON' button on the Vario joystick for sticking, physical damage, or lack of tactile feedback.

2. 2

   Use the Fendt transmission control circuit diagram (specifically Sheet 5 for cruise control) to trace the wiring from the joystick to the MFA circuit board.

3. 3

   Verify that the A039 MFA is communicating properly with the A050 basic control unit. (Note: If the whole armrest is failing to report, you will typically see a 00.0.03 bus fault instead).

4. 4

   Call up the fault code menu on the multiple display to confirm if the fault is currently active or stored in the history.

1. 1

   Power Down

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

2. 2

   Access the Joystick

   Carefully disassemble the upper housing of the A039 multifunction armrest to access the Vario joystick base and its wiring harness.

3. 3

   Inspect the Circuit Board

   Examine the Vario joystick CAN circuit board and the specific microswitch for the cruise control button. Look for broken solder joints, moisture ingress, or worn contacts.

4. 4

   Repair or Replace

   If the button itself is physically broken, aftermarket replacement buttons (color-coded red/green) can sometimes be swapped into the housing. If the internal CAN circuit board has failed, the joystick must be sent to a specialized agricultural electronics repair service (e.g., Ilgenfritz Mechatronics) for board repair. If the joystick is beyond repair, replace the entire Vario joystick assembly.

5. 5

   Reassembly

   Reconnect the joystick harness, reassemble the armrest, and reconnect the battery.

6. 6

   Clear Faults

   Use the terminal buttons (pressing A, B, and C simultaneously on the multiple display) or FENDIAS diagnostic software to clear the fault memory in the A050 ECU.

7. 7

   Test Drive

   Operate the tractor and engage the Tempomat cruise control to verify the signal fault does not return.